U.S. patent application number 15/161326 was filed with the patent office on 2016-09-15 for programmable logic device and method for manufacturing semiconductor device.
The applicant listed for this patent is Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Yoshiyuki KUROKAWA.
Application Number | 20160268265 15/161326 |
Document ID | / |
Family ID | 48944901 |
Filed Date | 2016-09-15 |
United States Patent
Application |
20160268265 |
Kind Code |
A1 |
KUROKAWA; Yoshiyuki |
September 15, 2016 |
PROGRAMMABLE LOGIC DEVICE AND METHOD FOR MANUFACTURING
SEMICONDUCTOR DEVICE
Abstract
To provide a programmable logic device in which the number of
elements per bit in a memory array can be reduced and with which
power consumption or operation frequency can be estimated
accurately at a testing stage. Provided is a programmable logic
device including a plurality of programmable logic elements and a
memory array which stores configuration data that determines logic
operation executed in the plurality of programmable logic elements.
The memory array includes a plurality of memory elements. The
memory element includes a node which establishes electrical
connection between the programmable logic element and the memory
array, a switch for supplying charge whose amount is determined by
the configuration data to the node, holding the charge in the node,
or releasing the charge from the node, and a plurality of wirings.
Capacitance is formed between the node and the wiring.
Inventors: |
KUROKAWA; Yoshiyuki;
(Sagamihara, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Semiconductor Energy Laboratory Co., Ltd. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
48944901 |
Appl. No.: |
15/161326 |
Filed: |
May 23, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13754979 |
Jan 31, 2013 |
9379113 |
|
|
15161326 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 27/1116 20130101;
H03K 19/1735 20130101; H03K 19/17728 20130101; H01L 21/82 20130101;
H01L 27/1225 20130101; H03K 19/1776 20130101; H01L 27/0207
20130101; H01L 27/105 20130101; H01L 27/1108 20130101; H01L
27/11898 20130101; H01L 28/40 20130101; H03K 19/17748 20130101;
H03K 19/1737 20130101; H01L 27/11807 20130101; H03K 19/0008
20130101 |
International
Class: |
H01L 27/11 20060101
H01L027/11; H01L 27/12 20060101 H01L027/12; H03K 19/00 20060101
H03K019/00; H03K 19/173 20060101 H03K019/173; H01L 49/02 20060101
H01L049/02; H01L 27/118 20060101 H01L027/118; H03K 19/177 20060101
H03K019/177 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 9, 2012 |
JP |
2012-026105 |
Claims
1. A semiconductor device comprising: a programmable logic element;
and a memory element comprising: an electrode electrically
connected to the programmable logic element; an insulating film
over the electrode; a first wiring over the electrode and the
insulating film; and a second wiring over the electrode and the
insulating film.
2. The semiconductor device according to claim 1, wherein the
memory element comprises a contact in the insulating film, wherein
the electrode is electrically connected to one of the first wiring
and the second wiring through the contact depending on
configuration data, wherein the memory element is configured to
supply a voltage corresponding to the configuration data from the
electrode to the programmable logic element, and wherein the
programmable logic element is configured to execute an operation
determined by the voltage corresponding to the configuration
data.
3. The semiconductor device according to claim 2, wherein the first
wiring is configured to supply a first voltage, and wherein the
second wiring is configured to supply a second voltage.
4. The semiconductor device according to claim 1, wherein the
memory element comprises a switch comprising a terminal
electrically connected to the electrode.
5. The semiconductor device according to claim 4, wherein the
memory element is configured to store configuration data, wherein
the memory element is configured to supply a voltage corresponding
to the configuration data from the electrode to the programmable
logic element, and wherein the programmable logic element is
configured to execute an operation determined by the voltage
corresponding to the configuration data.
6. The semiconductor device according to claim 5, wherein a first
capacitance is formed between the electrode and the first wiring
and is configured to hold first charge corresponding to the
configuration data, and wherein a second capacitance is formed
between the electrode and the second wiring and is configured to
hold second charge corresponding to the configuration data.
7. The semiconductor device according to claim 6, wherein the first
wiring is configured to supply a first voltage, and wherein the
second wiring is configured to supply a second voltage.
8. The semiconductor device according to claim 4, wherein the
switch comprises a transistor whose off-state current is smaller
than about 40 fA when a drain voltage is 3.3 V.
9. The semiconductor device according to claim 4, wherein the
switch comprises a transistor comprising an oxide semiconductor in
a channel formation region.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 13/754,979, filed Jan. 31, 2013, now allowed, which claims the
benefit of a foreign priority application filed in Japan as Serial
No. 2012-026105 on Feb. 9, 2012, both of which are incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a programmable logic device
with which the configuration of hardware can be changed and a
method for manufacturing a semiconductor device using the
programmable logic device.
[0004] 2. Description of the Related Art
[0005] In a semiconductor device called a programmable logic device
(PLD), a logic circuit is composed of an adequate number of
programmable logic elements (basic blocks), and the function of
each programmable logic element and interconnections between the
programmable logic elements can be changed after manufacture. PLDs
show flexibility in a reduction in development period and a change
in design specification as compared with conventional application
specific integrated circuits (ASICs) and gate arrays, which is
advantageous, thus being widely used in recent years.
[0006] The PLD needs a memory device for storing data
(configuration data) on the function of each programmable logic
element and the connections between the programmable logic
elements. This makes it difficult to avoid an increase in circuit
size and cost per chip of the PLD; thus, PLDs are often employed
for production of a prototype or small-quantity production.
Meanwhile, a method for reducing the cost per chip is proposed in
which a photomask corresponding to a circuit configuration that is
tested with a PLD is formed and an ASIC is manufactured therewith.
This method makes it possible to provide a semiconductor device
with desired specifications at relatively low cost by changing only
masks for the upper few layers as in gate arrays.
[0007] Non-Patent Document 1 below proposes a configuration in
which an SRAM for storing configuration data is formed using
polysilicon TFTs over a CMOS logic circuit functioning as a
programmable logic element and, after configuration data is
determined, an ASIC is manufactured with a new photomask
corresponding to the data. The ASIC does not include the SRAM and
has only the CMOS logic circuit on the chip; thus, an increase in
circuit size can be suppressed.
REFERENCE
Non-Patent Document
[0008] [Non-Patent Document 1] T. Naito et al., "World's first
monolithic 3D-FPGA with TFT SRAM over 90 nm 9 layer Cu CMOS", 2010
Symposium on VLSI Technology Digest of Technical Papers, 2010, pp.
219-220.
SUMMARY OF THE INVENTION
[0009] However, in the configuration of Non-Patent Document 1, the
SRAM having a large number of elements per bit is formed over the
CMOS logic circuit; thus, defects are likely to be caused, which
makes it difficult to manufacture a PLD with high yield.
[0010] Moreover, an SRAM composed of polysilicon TFTs not only
consumes power in an operating state, but also consumes more than a
little power in a non-operating state owing to the off-state
current of the polysilicon TFTs, and power consumed by the PLD
includes the power consumed by the SRAM. Therefore, power
consumption of a semiconductor device that is manufactured based on
the PLD cannot be estimated accurately at the stage of testing the
PLD.
[0011] Further, the SRAM composed of polysilicon TFTs is replaced
with wirings in manufacture of a semiconductor device based on the
PLD; thus, the layout of a layer over the CMOS logic circuit is
greatly changed. Therefore, operation delay and power consumption
due to parasitic capacitance between various wirings also cannot be
estimated accurately at the stage of testing the PLD.
[0012] In view of the foregoing technical background, an object of
one embodiment of the present invention is to provide a
programmable logic device in which the number of elements per bit
in a memory array can be reduced. Another object of one embodiment
of the present invention is to provide a programmable logic device
with which power consumption or operation frequency can be
estimated accurately at a testing stage.
[0013] Another object of one embodiment of the present invention is
to provide a method for manufacturing a semiconductor device which
enables power consumption or operation frequency to be estimated
accurately at the stage of testing with a programmable logic
device.
[0014] In one embodiment of the present invention, in a
programmable logic device, a memory array which stores
configuration data is provided over a plurality of programmable
logic elements which compose a logic circuit in accordance with the
configuration data. The programmable logic elements are
electrically connected to the memory array. A plurality of memory
elements included in the memory array each include a node which
establishes electrical connection between the programmable logic
element and the memory array, a switch for supplying charge whose
amount is determined by the configuration data to the node, holding
the charge in the node, or releasing the charge from the node, and
a plurality of wirings. Capacitance is formed between the node and
the wiring.
[0015] In one embodiment of the present invention, only one
transistor, which composes a switch, needs to be provided in each
memory element. Therefore, the number of elements per bit can be
reduced as compared with the case where an SRAM is used as a memory
array.
[0016] In the above programmable logic device, the logic circuit
that is composed of the plurality of programmable logic elements
varies depending on the configuration data. In one embodiment of
the present invention, after determination of the configuration
data, a plurality of wirings are formed over a plurality of
programmable logic elements, which are additionally prepared, to be
connected to the plurality of programmable logic elements in
accordance with the configuration data, whereby a semiconductor
device is manufactured.
[0017] In one embodiment of the present invention, a semiconductor
device is manufactured by replacement of a memory array provided in
the upper layer of a programmable logic device with a plurality of
wirings. In one embodiment of the present invention, the memory
array of the programmable logic device already includes the
plurality of wirings; accordingly, the difference in parasitic
capacitance generated between the programmable logic elements in
the lower layer and the wirings in the upper layer can be reduced
between the programmable logic device and the semiconductor device.
Therefore, power consumption or operation frequency of the
semiconductor device due to the parasitic capacitance can be
estimated accurately by testing of the programmable logic
device.
[0018] As another feature of the present invention, a switch
provided in a memory element may be composed of a transistor with
small off-state current in one embodiment of the present invention.
For example, a transistor including, in a channel formation region,
a semiconductor which has a wide band gap and is highly purified by
reduction of impurities serving as electron donors (donors), such
as moisture or hydrogen, and by reduction of oxygen vacancies has
extremely small off-state current. In one embodiment of the present
invention, the above transistor is used as a switch, whereby
leakage of charge held in a node can be prevented. Accordingly,
power consumption of the memory array due to the off-state current
of a transistor can be reduced as compared with the case where an
SRAM composed of polysilicon TFTs is used. Therefore, power
consumption of the semiconductor device manufactured based on the
programmable logic device can be estimated accurately at the stage
of testing the programmable logic device.
[0019] Specifically, a programmable logic device according to one
embodiment of the present invention includes a plurality of
programmable logic elements and a memory array which stores
configuration data that determines logic operation executed in the
plurality of programmable logic elements. The memory array includes
a plurality of memory elements. The memory element includes a node
which establishes electrical connection between the programmable
logic element and the memory array, a switch for supplying charge
whose amount is determined by the configuration data to the node,
holding the charge in the node, or releasing the charge from the
node, and a plurality of wirings. Capacitance is formed between the
node and the wiring.
[0020] Specifically, a programmable logic device according to one
embodiment of the present invention includes a plurality of
programmable logic elements, a wiring array, and a memory array
which stores configuration data that determines logic operation
executed in the plurality of programmable logic elements or
connections between the plurality of programmable logic elements
established by the wiring array. The memory array includes a
plurality of memory elements. The memory element includes a node
which establishes electrical connection between the programmable
logic element and the memory array, a switch for supplying charge
whose amount is determined by the configuration data to the node,
holding the charge in the node, or releasing the charge from the
node, and a plurality of wirings. Capacitance is formed between the
node and the wiring.
[0021] Specifically, in a method for manufacturing a semiconductor
device according to one embodiment of the present invention, over a
plurality of first programmable logic elements, a memory array
which stores configuration data that determines logic operation
executed in the plurality of first programmable logic elements is
formed, so that a programmable logic device is formed; and over a
plurality of second programmable logic elements, a plurality of
wirings connected to the plurality of second programmable logic
elements in accordance with the configuration data are formed after
determination of the configuration data in the programmable logic
device. The memory array includes a plurality of memory elements.
The memory element includes a node which establishes electrical
connection between the first programmable logic element and the
memory array, a switch for supplying charge whose amount is
determined by the configuration data to the node, holding the
charge in the node, or releasing the charge from the node, and a
plurality of wirings. Capacitance is formed between the node and
the wiring.
[0022] According to one embodiment of the present invention, a
programmable logic device in which the number of elements per bit
in a memory array can be reduced can be provided. According to one
embodiment of the present invention, a programmable logic device
with which power consumption or operation frequency can be
estimated accurately at a testing stage can be provided. According
to one embodiment of the present invention, a method for
manufacturing a semiconductor device which enables power
consumption or operation frequency to be estimated accurately at
the stage of testing with a programmable logic device can be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIGS. 1A and 1B illustrate a configuration of a programmable
logic device.
[0024] FIGS. 2A and 2B each illustrate a configuration of a
programmable logic element.
[0025] FIGS. 3A and 3B illustrate a configuration of a
semiconductor device.
[0026] FIGS. 4A and 4B illustrate a configuration of a logic array
and a configuration a switch.
[0027] FIG. 5 illustrates a configuration of the lower layer of a
programmable logic device.
[0028] FIGS. 6A and 6B illustrate a configuration of a memory
element and connection between a wiring and a node.
[0029] FIGS. 7A and 7B illustrate a configuration of a memory
element and connection between a wiring and a node.
[0030] FIG. 8 is a block diagram illustrating a configuration of a
memory array.
[0031] FIG. 9 illustrates connections between a memory element, a
sense amplifier, a precharge circuit, a switch circuit, and a main
amplifier.
[0032] FIG. 10 is a timing chart.
[0033] FIGS. 11A to 11C are circuit diagrams of a look-up
table.
[0034] FIGS. 12A to 12D illustrate a method for manufacturing a
PLD.
[0035] FIGS. 13A to 13C illustrate a method for manufacturing a
PLD.
[0036] FIGS. 14A to 14C illustrate a method for manufacturing a
PLD.
[0037] FIG. 15 is a cross-sectional view of a semiconductor
device.
[0038] FIGS. 16A to 16F each illustrate an electronic device.
[0039] FIGS. 17A and 17B illustrate the layout of memory elements
and the layout of conductive films.
[0040] FIGS. 18A and 18B illustrate the layout of memory elements
and the layout of conductive films.
[0041] FIGS. 19A and 19B illustrate the layout of memory elements
and the layout of conductive films.
[0042] FIGS. 20A and 20B illustrate the layout of memory elements
and the layout of conductive films.
DETAILED DESCRIPTION OF THE INVENTION
[0043] Hereinafter, embodiments of the present invention will be
described in detail with reference to the accompanying drawings.
However, the present invention is not limited to the following
description and it is easily understood by those skilled in the art
that the mode and details can be variously changed without
departing from the scope and spirit of the present invention.
Therefore, the present invention should not be construed as being
limited to the description in the following embodiments.
[0044] Note that a semiconductor device of the present invention
includes, in its category, various semiconductor integrated
circuits formed using semiconductor elements, such as
microprocessors, image processing circuits, controllers for
semiconductor display devices, digital signal processors (DSPs),
micro controllers, and the like. In addition, the semiconductor
device of the present invention also includes, in its category,
various devices formed using the above semiconductor integrated
circuits, such as RF tags, semiconductor display devices, and the
like. The semiconductor display devices include, in its category,
liquid crystal display devices, light-emitting devices in which a
light-emitting element typified by an organic light-emitting
element (OLED) is provided for each pixel, electronic paper,
digital micromirror devices (DMDs), plasma display panels (PDPs),
field emission displays (FEDs), and other semiconductor display
devices in which a semiconductor element is included in a driver
circuit.
Embodiment 1
[0045] FIG. 1A schematically illustrates a configuration example of
a PLD according to one embodiment of the present invention. A PLD
100 illustrated in FIG. 1A includes a logic array 102 including a
plurality of programmable logic elements (PLEs) 101 and a memory
array 104 including a plurality of memory elements 103. The memory
array 104 is provided over a layer in which the logic array 102 is
formed.
[0046] Each PLE 101 is a logic element whose logic operation, i.e.,
an output value corresponding to an input value, is determined by
configuration data 105. Determination of the logic operation
executed by each PLE 101 by the configuration data 105 results in
determination of the function of a logic circuit that is configured
in the logic array 102.
[0047] The memory array 104 has a function of storing the
configuration data 105. The memory array 104 is provided with a
plurality of wirings for supplying power supply potential to each
memory element 103. FIG. 1A illustrates, as an example, the case
where the memory array 104 is provided with a wiring 108 and a
wiring 109.
[0048] FIG. 1B schematically illustrates a specific configuration
example of the memory element 103 and an example of connections
between the memory elements 103 and the PLEs 101. Note that FIG. 1B
illustrates, as an example, the case where a memory element 103a
and a memory element 103b, which correspond to two of the plurality
of memory elements 103, are assigned to one of the PLEs 101.
[0049] As exemplified by the memory elements 103a and 103b in FIG.
1B, the memory element 103 includes a switch 106 and wirings 107 to
109. The wiring 107 has a function of transmitting the
configuration data 105 to each memory element 103. The wirings 108
and 109 each have a function of supplying power supply potential to
each memory element 103. In FIG. 1B, each memory element 103
includes the wiring 108 for supplying a high-level power supply
potential to the memory element 103 and the wiring 109 for
supplying a low-level power supply potential to the memory element
103; however, the number of wirings for supplying power supply
potential to each memory element 103 may be three or more.
[0050] Electrical connection between the PLE 101 and the memory
element 103 is established by a node 110. In the memory element
103, capacitance is formed between the node 110 and each of the
wirings 108 and 109. In FIG. 1B, the capacitance formed between the
node 110 and the wiring 108 is shown as a capacitor 111, and the
capacitance formed between the node 110 and the wiring 109 is shown
as a capacitor 112.
[0051] Note that the term "connection" in this specification refers
to electrical connection and corresponds to the state in which
current, voltage, or a potential can be supplied or transmitted.
Accordingly, a connection state means not only a state of direct
connection but also a state of indirect connection through an
element such as a wiring, a resistor, a diode, or a transistor so
that current, voltage, or a potential can be supplied or
transmitted.
[0052] The configuration data 105 that is transmitted through the
wiring 107 is written into the node 110 via the switch 106.
Specifically, charge whose amount is determined by the
configuration data 105 is supplied through the wiring 107 to the
node 110, the capacitor 111, and the capacitor 112 via the switch
106 that is turned on (put in a conduction state), whereby the
configuration data 105 is written into the node 110. Next, the
switch 106 is turned off (put in a non-conduction state), and the
charge is held in the node 110, the capacitor 111, and the
capacitor 112, whereby the configuration data 105 is held in the
memory element 103. Then, the switch 106 is turned on again,
whereby the charge held in the node 110, the capacitor 111, and the
capacitor 112 can be released to the wiring 107.
[0053] The configuration data 105 is transmitted from the memory
element 103 to the PLE 101 through the node 110. In FIG. 1B, the
configuration data 105 is transmitted from the memory elements 103a
and 103b to one PLE 101; however, the configuration data 105 may be
transmitted from one memory element 103 or three or more memory
elements 103 to one PLE 101.
[0054] FIG. 2A illustrates one mode of the PLE 101. The PLE 101
illustrated in FIG. 2A includes a look-up table (LUT) 113 and a
register 114. Logic operation executed by the LUT 113 varies
depending on the configuration data 105. Determination of the
configuration data 105 results in determination of one output value
corresponding to plural input values of the LUT 113. An output
signal including the output value is output from the LUT 113. The
register 114 holds the output signal from the LUT 113 and outputs a
signal corresponding the output signal in synchronization with a
clock signal CLK.
[0055] Note that the PLE 101 may include a multiplexer circuit with
which selection can be made whether the output signal from the LUT
113 goes through the register 114 or not.
[0056] Further, the type of the register 114 may be determined by
the configuration data 105. Specifically, the register 114 may have
a function of any of a D register, a T register, a JK register, and
an RS register depending on the configuration data 105.
[0057] The PLE 101 may also include a memory device (configuration
memory) for storing the configuration data 105 transmitted from the
memory element 103. The PLE 101 in FIG. 2B has a structure in which
a configuration memory 115 is added to the PLE 101 in FIG. 2A. With
the configuration memory 115, the operation of determining again
the logic operation executed in the PLE 101 in accordance with the
same configuration data 105 can be performed at high speed as
compared with the case where the configuration data 105 that is
transmitted directly from the memory element 103 is used.
[0058] In one embodiment of the present invention, after
determination of the configuration data 105, a plurality of wirings
are formed over another logic array 102 to be connected to the
plurality of PLEs 101 in accordance with the configuration data
105, whereby a semiconductor device is manufactured.
[0059] FIG. 3A schematically illustrates a configuration example of
a semiconductor device 120 according to one embodiment of the
present invention. The semiconductor device 120 in FIG. 3A is
similar to the PLD 100 in FIG. 1A in including the logic array 102
that includes the plurality of PLEs 101. However, the semiconductor
device 120 differs from the PLD 100 in FIG. 1A in that, instead of
the memory array 104, a plurality of wirings corresponding to the
plurality of wirings used for supply of power supply potential in
the memory array 104 are provided over the layer in which the logic
array 102 is formed.
[0060] FIG. 3A illustrates, as an example, the case where the
wirings 108 and 109 are provided over the logic array 102 as the
plurality of wirings corresponding to the plurality of wirings used
for supply of power supply potential.
[0061] FIG. 3B schematically illustrates an example of connections
between the PLEs 101 and the wirings 108 and 109. Note that FIG. 3B
illustrates the case where the memory elements 103a and 103b in
FIG. 1B are each replaced with the wirings 108 and 109.
[0062] In the semiconductor device according to one embodiment of
the present invention, one of the wirings 108 and 109 which is
selected in accordance with the configuration data 105 is connected
to the PLE 101 through the node 110. Specifically, in the case
exemplified in FIG. 3B, the wiring 108 is selected from the wirings
108 and 109, which are provided instead of the memory element 103a,
to be connected to the PLE 101 through the node 110. Further, the
wiring 109 is selected from the wirings 108 and 109, which are
provided instead of the memory element 103b, to be connected to the
PLE 101 through the node 110.
[0063] The logic operation of the PLE 101 is determined by the
power supply potentials supplied from the wirings 108 and 109.
Determination of the logic operation executed by each PLE 101
results in determination of the function of a logic circuit that is
configured in the logic array 102.
[0064] In one embodiment of the present invention, the
semiconductor device 120 is manufactured by replacement of the
memory array 104 provided in the upper layer of the PLD 100 with a
plurality of wirings, e.g., the wirings 108 and 109. In one
embodiment of the present invention, the memory array 104 of the
PLD 100 already includes the plurality of wirings. Accordingly, the
difference in parasitic capacitance generated between the logic
array 102 in the lower layer and the plurality of wirings in the
upper layer can be reduced between the PLD 100 and the
semiconductor device 120. Therefore, power consumption or operation
frequency of the semiconductor device 120 due to the parasitic
capacitance can be estimated accurately by testing of the PLD
100.
[0065] Note that not only the logic operation executed by the PLE
101 but also the connections between the PLEs 101 are determined by
the configuration data 105. Specifically, the connections between
the PLEs 101 are established by a wiring array provided in the
logic array 102. The wiring array includes a wiring group including
a plurality of wirings and switches for controlling connections
between the wirings belonging to the wiring group.
[0066] FIG. 4A schematically illustrates, as an example, part of
the configuration of the logic array 102. The logic array 102
illustrated in FIG. 4A includes the plurality of PLEs 101, a wiring
group 121 connected to any of the plurality of PLEs 101, and
switches 122 for controlling connections between the wirings
belonging to the wiring group 121. The wiring group 121 and the
switches 122 correspond to a wiring array 123. The connections
between the wirings controlled by the switches 122 are determined
by the configuration data 105.
[0067] FIG. 4B illustrates a configuration example of the switch
122. The switch 122 illustrated in FIG. 4B has a function of
controlling connections between a wiring 125 and a wiring 126 which
belong to the wiring group 121. Specifically, the switch 122
includes transistors 127 to 132. The transistor 127 has a function
of controlling electrical connection between a point A of the
wiring 125 and a point C of the wiring 126. The transistor 128 has
a function of controlling electrical connection between a point B
of the wiring 125 and the point C of the wiring 126. The transistor
129 has a function of controlling electrical connection between the
point A of the wiring 125 and a point D of the wiring 126. The
transistor 130 has a function of controlling electrical connection
between the point B of the wiring 125 and the point D of the wiring
126. The transistor 131 has a function of controlling electrical
connection between the point A and the point B of the wiring 125.
The transistor 132 has a function of controlling electrical
connection between the point C and the point D of the wiring
126.
[0068] The selection between on and off (switching) of each of the
transistors 127 to 132 is determined by the configuration data 105
that is held in the memory array 104. Specifically, in the PLD 100,
gate electrodes of the transistors 127 to 132 are connected to the
respective memory elements 103 through the nodes 110. In the
semiconductor device 120, the gate electrodes of the transistors
127 to 132 are connected to the wiring 108 or the wiring 109
through the nodes 110.
[0069] The switches 122 also have a function of controlling
electrical connection between the wiring group 121 and output
terminals 124 of the logic array 102. The output terminals 124 are
connected to a circuit group other than the logic array 102 and the
memory array 104 included in the PLD 100.
[0070] FIG. 5 illustrates an example of the configuration of a
layer under the memory array 104 in the PLD 100. In FIG. 5, I/O
elements 140, phase lock loops (PLLs) 141, a RAM 142, and a
multiplier 143 are provided besides the logic array 102 in the
layer under the memory array 104. The I/O element 140 functions as
an interface which controls input/output of a signal from/to an
external circuit of the PLD 100. The PLL 141 has a function of
generating a clock signal CLK. The RAM 142 has a function of
storing data used for logic operation. The multiplier 143
corresponds to a logic circuit for multiplication. When the logic
array 102 includes a function of executing multiplication, the
multiplier 143 is not necessarily provided.
[0071] FIG. 6A schematically illustrates a specific configuration
example of the memory element 103. Note that FIG. 6A illustrates
the memory element 103a and the memory element 103b, which
correspond to two of the plurality of memory elements 103.
[0072] As exemplified by the memory elements 103a and 103b in FIG.
6A, the memory element 103 includes a transistor 106t functioning
as the switch 106, the wirings 107 to 109, and a wiring 150.
Specifically, a gate electrode of the transistor 106t is connected
to the wiring 150. One of a source terminal and a drain terminal of
the transistor 106t is connected to the wiring 107, and the other
is connected to the node 110.
[0073] Note that a "source terminal" of a transistor means a source
region that is part of an active layer or a source electrode that
is connected to an active layer. Similarly, "drain terminal" of a
transistor means a drain region that is a part of an active layer
or a drain electrode connected to an active layer.
[0074] The tennis "source terminal" and "drain terminal" of a
transistor interchange with each other depending on the type of the
channel of the transistor or levels of potentials applied to the
terminals. In general, in an n-channel transistor, a terminal to
which a low potential is applied is called a source terminal, and a
terminal to which a high potential is applied is called a drain
terminal. Further, in a p-channel transistor, a terminal to which a
low potential is applied is called a drain terminal, and a terminal
to which a high potential is applied is called a source terminal.
In this specification, although the connection relation of the
transistor is described assuming that the source terminal and the
drain terminal are fixed in some cases for convenience, actually,
the names of the source terminal and the drain terminal interchange
with each other depending on the relation of the potentials.
[0075] Capacitance is faulted between the node 110 and each of the
wirings 108 and 109. In FIG. 6A, the capacitance formed between the
node 110 and the wiring 108 is shown as the capacitor 111, and the
capacitance formed between the node 110 and the wiring 109 is shown
as the capacitor 112. The configuration data 105 is output from the
memory element 103 through the node 110.
[0076] FIG. 6B illustrates a state where the memory elements 103a
and 103b in FIG. 6A are each replaced with the wirings 108 and 109.
In the case exemplified in FIG. 6B, the wiring 108 is selected from
the wirings 108 and 109, which are provided instead of the memory
element 103a, by the configuration data 105 to be connected to the
node 110. Further, the wiring 109 is selected from the wirings 108
and 109, which are provided instead of the memory element 103b, by
the configuration data 105 to be connected to the node 110.
[0077] FIG. 7A schematically illustrates a specific configuration
example of the memory element 103, which is different from that in
FIG. 6A. Note that FIG. 7A illustrates the memory element 103a and
the memory element 103b, which correspond to two of the plurality
of memory elements 103.
[0078] As exemplified by the memory elements 103a and 103b in FIG.
7A, the memory element 103 includes the transistor 106t functioning
as the switch 106, the wirings 107 to 109, the wiring 150, and a
transistor 151t. Specifically, the gate electrode of the transistor
106t is connected to the wiring 150. One of the source terminal and
the drain terminal of the transistor 106t is connected to the
wiring 107, and the other is connected to the node 110. A gate
electrode of the transistor 151t is connected to the node 110. One
of a source terminal and a drain terminal of the transistor 151t is
connected to the wiring 107, and the other is connected to a node
to which a fixed potential such as a ground potential is
supplied.
[0079] Capacitance is formed between the node 110 and each of the
wirings 108 and 109. In FIG. 7A, the capacitance formed between the
node 110 and the wiring 108 is shown as the capacitor 111, and the
capacitance formed between the node 110 and the wiring 109 is shown
as the capacitor 112. The configuration data 105 is output from the
memory element 103 through the node 110. Further, in response to a
request from an external circuit, the configuration data 105 held
in the memory element 103 can be read out through the transistor
151t.
[0080] FIG. 7B illustrates a state where the memory elements 103a
and 103b in FIG. 7A are each replaced with the wirings 108 and 109.
In the case exemplified in FIG. 7B, the wiring 108 is selected from
the wirings 108 and 109, which are provided instead of the memory
element 103a, by the configuration data 105 to be connected to the
node 110. Further, the wiring 109 is selected from the wirings 108
and 109, which are provided instead of the memory element 103b, by
the configuration data 105 to be connected to the node 110.
[0081] Note that the memory element 103 exemplified in FIG. 6A or
FIG. 7A may further include another circuit element such as a
transistor, a diode, a resistor, a capacitor, or an inductor as
needed.
[0082] FIG. 6A and FIG. 7A each illustrate the case where the
transistor 106t includes the gate electrode only on one side of an
active layer. When the transistor 106t includes a pair of gate
electrodes between which the active layer is provided, one of the
gate electrodes is supplied with a signal for controlling
switching, and the other of the gate electrodes may be in a
floating state (i.e., electrically isolated) or may be supplied
with a potential. In the latter case, potentials with the same
level may be supplied to the pair of electrodes, or a fixed
potential such as a ground potential may be supplied only to the
other of the gate electrodes. By controlling the level of a
potential supplied to the other of the gate electrodes, the
threshold voltage of the transistor 106t can be controlled.
[0083] Further, in the memory element 103 exemplified in FIG. 6A or
FIG. 7A, the transistor 106t is used as the switch 106; however,
one embodiment of the present invention is not limited to this
structure. A plurality of transistors may be used as the switch
106. In the case where a plurality of transistors function as the
switch 106, the plurality of transistors may be connected to each
other in parallel, in series, or in combination of parallel
connection and series connection.
[0084] In this specification, a state in which transistors are
connected to each other in series means, for example, a state in
which only one of a source terminal and a drain terminal of a first
transistor is connected to only one of a source terminal and a
drain terminal of a second transistor. In addition, a state in
which transistors are connected to each other in parallel means a
state in which one of a source terminal and a drain terminal of a
first transistor is connected to one of a source terminal and a
drain terminal of a second transistor and the other of the source
terminal and the drain terminal of the first transistor is
connected to the other of the source terminal and the drain
terminal of the second transistor.
[0085] In one embodiment of the present invention, an amorphous,
microcrystalline, polycrystalline, or single crystal semiconductor
(e.g., silicon or germanium) or a wide bandgap semiconductor such
as an oxide semiconductor may be used for the active layer of the
transistor 106t. As silicon, any of the following can be used:
amorphous silicon formed by a sputtering method or a vapor
deposition method such as a plasma CVD method; polycrystalline
silicon obtained in such a manner that amorphous silicon is
crystallized by laser annealing or the like; single crystal silicon
obtained in such a manner that a surface portion of a single
crystal silicon wafer is separated by implantation of hydrogen ions
or the like into the silicon wafer; and the like.
[0086] Note that in Non-Patent Document 1, according to FIG. 11 and
FIG. 14, off-state current of TFTs which compose an SRAM is about 1
pA when the voltage (drain voltage) between a source terminal and a
drain terminal is 3.3 V. Thus, in Non-Patent Document 1, a power
W.sub.SRAM consumed by the SRAM for holding data can be estimated
to be about 6.6 pW.
[0087] The capacitance value of a capacitor that is used in a
general DRAM is said to be about 20 fF (Y. Yanagawa, T. Sekiguchi,
A. Kotabe, K. Ono, and R. Takemura, "In--substrate-bitline Sense
Amplifier with Array-noise-gating Scheme for Low-noise 4F.sup.2
DRAM Array Operable at 10-fF Cell Capacitance", 2011 Symposium on
VLSI Circuits Digest of Technical Papers, pp. 230-231.). Parasitic
capacitance of a wiring which allows the amount of charge held in
the capacitor to be read out is estimated to be about 1 pF, which
is 50 times 20 fF, at most. Considered is the case where, in a
memory array according to one embodiment of the present invention,
a capacitance value C.sub.107 of parasitic capacitance applied to
the wiring 107 is 1 pF, a high-level potential V.sub.data of a
signal including configuration data is 3.3 V, and refreshing is
performed N times every second. In this case, a power W.sub.107
consumed for setting the potential of the wiring 107 to V.sub.data
is represented by
(1/2).times.C.sub.107.times.V.sub.data.sup.2.times.N, and can be
estimated to be about 5.4N pW. Accordingly, it is necessary to set
N smaller than about 1.2, that is, to set the refresh interval
(refresh cycle) t longer than about 0.8 seconds, in order to make
the consumed power W.sub.107 smaller than the consumed power
W.sub.SRAM.
[0088] Considered is the case where, in the memory array according
to one embodiment of the present invention, a high-level power
supply potential VDD that is supplied to the memory element 103
through the wiring 108 is set to 3.3 V and refreshing is performed
when the potential of the node 110 falls to half of 3.3 V. A
capacitance value C.sub.111 of the capacitor 111 is set to 20 fF,
which is equivalent to that in a general DRAM. When the off-state
current of the transistor 106t is represented by I.sub.off and the
refresh interval (refresh cycle) is represented by t,
t=C.sub.111.times.VDD.times.(1/2)/I.sub.off=33 fF/I.sub.off is
satisfied. Accordingly, it is necessary to set I.sub.off smaller
than about 40 fA in order to make t longer than about 0.8
seconds.
[0089] In one embodiment of the present invention, the off-state
current of a transistor used as the switch 106 is smaller than 40
fA when the drain voltage is 3.3 V; thus, charge held in the node
110 does not easily leak, which allows extension of the interval
between operations of writing the configuration data that is stored
in the memory array 104 into the memory array 104 again
(refreshing). When the refresh interval is long, i.e., the
frequency of refreshing per unit time is low, power consumed for
the refreshing can be reduced, so that power consumption of the
semiconductor device 120 that is manufactured based on the PLD 100
can be estimated accurately at the stage of testing the PLD
100.
[0090] Note that when the transistor 106t includes a wide bandgap
semiconductor such as an oxide semiconductor in a channel formation
region, the transistor 106t can have extremely small off-state
current and high withstand voltage. Further, when the transistor
106t having the above structure is used as the switch 106 of the
memory element 103, leakage of charge accumulated in the node 110,
the capacitor 111, and the capacitor 112 can be prevented
effectively as compared with the case where a transistor including
a normal semiconductor such as silicon or germanium is used.
[0091] Unless otherwise specified, in the case of an n-channel
transistor, the off-state current in this specification is a
current which flows between a source terminal and a drain terminal
when, in the state where the potential of the drain terminal is
higher than that of the source terminal and that of a gate
electrode, the potential of the gate electrode is lower than or
equal to 0 V with respect to the potential of the source terminal.
Alternatively, in this specification, in the case of a p-channel
transistor, the off-state current is a current which flows between
a source terminal and a drain terminal when, in the state where the
potential of the drain terminal is lower than that of the source
terminal and that of a gate electrode, the potential of the gate
electrode is higher than or equal to 0 V with respect to the
potential of the source terminal.
[0092] An oxide semiconductor preferably contains at least indium
(In) or zinc (Zn). As a stabilizer for reducing variations in
electric characteristics of a transistor including the oxide
semiconductor, gallium (Ga) is preferably additionally contained.
Tin (Sn) is preferably contained as a stabilizer. Hafnium (Hf) is
preferably contained as a stabilizer. Aluminum (Al) is preferably
contained as a stabilizer. Zirconium (Zr) is preferably contained
as a stabilizer.
[0093] As another stabilizer, one or plural kinds of lanthanoid
such as lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium
(Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb),
dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium
(Yb), or lutetium (Lu) may be contained.
[0094] As the oxide semiconductor, for example, any of the
following can be used: indium oxide; tin oxide; zinc oxide; a
two-component metal oxide such as an In--Zn-based oxide, a
Sn--Zn-based oxide, an Al--Zn-based oxide, a Zn--Mg-based oxide, a
Sn--Mg-based oxide, an In--Mg-based oxide, or an In--Ga-based
oxide; a three-component metal oxide such as an In--Gap--Zn-based
oxide (also referred to as IGZO), an In--Al--Zn-based oxide, an
In--Sn--Zn-based oxide, a Sn--Ga--Zn-based oxide, an
Al--Ga--Zn-based oxide, a Sn--Al--Zn-based oxide, an
In--Hf--Zn-based oxide, an In--La--Zn-based oxide, an
In--Pr--Zn-based oxide, an In--Nd--Zn-based oxide, an
In--Sm--Zn-based oxide, an In--Eu--Zn-based oxide, an
In--Gd--Zn-based oxide, an In--Tb--Zn-based oxide, an
In--Dy--Zn-based oxide, an In--Ho--Zn-based oxide, an
In--Er--Zn-based oxide, an In--Tm--Zn-based oxide, an
In--Yb--Zn-based oxide, or an In--Lu--Zn-based oxide; a
four-component metal oxide such as an In--Sn--Ga--Zn-based oxide,
an In--Hf--Ga--Zn-based oxide, an In--Al--Ga--Zn-based oxide, an
In--Sn--Al--Zn-based oxide, an In--Sn--Hf--Zn-based oxide, or an
In--Hf--Al--Zn-based oxide.
[0095] Note that, for example, an In--Gap--Zn-based oxide means an
oxide containing In, Ga, and Zn, and there is no limitation on the
ratio of In, Ga, and Zn. Further, the In--Gap--Zn-based oxide may
contain a metal element other than In, Ga, and Zn. The
In--Gap--Zn-based oxide has sufficiently high resistance when no
electric field is applied thereto, so that off-state current can be
sufficiently reduced. Further, the In--Gap--Zn-based oxide has high
mobility.
[0096] For example, an In--Gap--Zn-based oxide with an atomic ratio
of In:Ga:Zn=1:1:1 (=1/3:1/3:1/3) or In:Ga:Zn=2:2:1 (=2/5:2/5:1/5),
or an oxide with an atomic ratio close to the above atomic ratios
can be used. Alternatively, an In--Sn--Zn-based oxide with an
atomic ratio of In:Sn:Zn=1:1:1 (=1/3:1/3:1/3), In:Sn:Zn=2:1:3
(=1/3:1/6:1/2 ), or In:Sn:Zn=2:1:5 (=1/4:1/8:5/8), or an oxide with
an atomic ratio close to the above atomic ratios may be used.
[0097] For example, high mobility can be obtained relatively easily
in the case of using an In--Sn--Zn-based oxide. However, mobility
can be increased by reducing the defect density in a bulk also in
the case of using an In--Gap--Zn-based oxide.
[0098] Note that a highly purified oxide semiconductor (a purified
oxide semiconductor) obtained by reduction of impurities such as
moisture or hydrogen which serve as electron donors (donors) and
reduction of oxygen vacancies is an intrinsic (i-type)
semiconductor or a substantially i-type semiconductor. Therefore, a
transistor including the oxide semiconductor has significantly
small off-state current. Furthermore, the band gap of the oxide
semiconductor is 2 eV or more, preferably 2.5 eV or more, further
preferably 3 eV or more. By using an oxide semiconductor film which
is highly purified by a sufficient reduction in the concentration
of impurities such as moisture and hydrogen and a reduction of
oxygen vacancies, the off-state current of the transistor can be
reduced.
[0099] Specifically, various experiments can prove small off-state
current of a transistor in which a highly purified oxide
semiconductor is used for a semiconductor film. For example, even a
transistor with a channel width of 1.times.10.sup.6 .mu.m and a
channel length of 10 .mu.m can have off-state current less than or
equal to the measurement limit of a semiconductor parameter
analyzer, that is, less than or equal to 1.times.10.sup.-13 A when
the voltage (drain voltage) between a source terminal and a drain
terminal ranges between 1 V and 10 V. In this case, off-state
current standardized on the channel width of the transistor is less
than or equal to 100 zA.quadrature..mu.m. Accordingly, it is
possible to make the off-state current of the transistor in which
an oxide semiconductor is used for a semiconductor film smaller
than 40 fA by setting the channel width smaller than
4.times.10.sup.5 .mu.m. In addition, a capacitor and a transistor
are connected to each other and the off-state current is measured
with a circuit in which charge flowing into or from the capacitor
is controlled by the transistor. In the measurement, a highly
purified oxide semiconductor film is used for a channel formation
region of the transistor, and the off-state current of the
transistor is measured from a change in the amount of charge of the
capacitor per unit time. As a result, it can be seen that, in the
case where the voltage between the source terminal and the drain
terminal of the transistor is 3 V, a smaller off-state current of
several tens of yoctoamperes per micrometer (yA/.mu.m) is obtained.
Accordingly, the transistor in which a highly purified oxide
semiconductor film is used for a channel formation region has much
smaller off-state current than a transistor including crystalline
silicon.
[0100] In one embodiment of the present invention, the use of the
transistor 106t with extremely small off-state current enables
leakage of charge from the node 110, the capacitor 111, and the
capacitor 112 to be prevented. Accordingly, power consumption of
the memory array 104 due to the off-state current of a transistor
can be reduced as compared with the case where an SRAM composed of
polysilicon TFTs is used. Therefore, power consumption of the
semiconductor device 120 that is manufactured based on the PLD 100
can be estimated accurately at the stage of testing the PLD
100.
[0101] An oxide semiconductor film may be in a non-single-crystal
state, for example. The non-single-crystal state is, for example,
structured by at least one of c-axis aligned crystal (CAAC),
polycrystal, microcrystal, and an amorphous part. The density of
defect states of an amorphous part is higher than those of
microcrystal and CAAC. The density of defect states of microcrystal
is higher than that of CAAC. Note that an oxide semiconductor
including CAAC is referred to as a CAAC-OS (c-axis aligned
crystalline oxide semiconductor).
[0102] For example, an oxide semiconductor film may include a
CAAC-OS. In the CAAC-OS, for example, c-axes are aligned, and
a-axes and/or b-axes are not macroscopically aligned.
[0103] For example, an oxide semiconductor film may include
microcrystal. Note that an oxide semiconductor including
microcrystal is referred to as a microcrystalline oxide
semiconductor. A microcrystalline oxide semiconductor film includes
microcrystal (also referred to as nanocrystal) with a size greater
than or equal to 1 nm and less than 10 nm, for example.
Alternatively, a microcrystalline oxide semiconductor film, for
example, includes a crystal-amorphous mixed phase structure where
crystal parts (each of which is greater than or equal to 1 nm and
less than 10 nm) are distributed.
[0104] For example, an oxide semiconductor film may include an
amorphous part. Note that an oxide semiconductor including an
amorphous part is referred to as an amorphous oxide semiconductor.
An amorphous oxide semiconductor film, for example, has disordered
atomic arrangement and no crystalline component. Alternatively, an
amorphous oxide semiconductor film is, for example, absolutely
amorphous and has no crystal part.
[0105] Note that an oxide semiconductor film may be a mixed film
including any of a CAAC-OS, a microcrystalline oxide semiconductor,
and an amorphous oxide semiconductor. The mixed film, for example,
includes a region of an amorphous oxide semiconductor, a region of
a microcrystalline oxide semiconductor, and a region of a CAAC-OS.
Further, the mixed film may have a stacked structure including a
region of an amorphous oxide semiconductor, a region of a
microcrystalline oxide semiconductor, and a region of a CAAC-OS,
for example.
[0106] Note that an oxide semiconductor film may be in a
single-crystal state, for example.
[0107] An oxide semiconductor film preferably includes a plurality
of crystal parts. In each of the crystal parts, a c-axis is
preferably aligned in a direction parallel to a normal vector of a
surface where the oxide semiconductor film is formed or a normal
vector of a surface of the oxide semiconductor film. Note that,
among crystal parts, the directions of the a-axis and the b-axis of
one crystal part may be different from those of another crystal
part. An example of such an oxide semiconductor film is a CAAC-OS
film.
[0108] The CAAC-OS film is not absolutely amorphous. The CAAC-OS
film, for example, includes an oxide semiconductor with a
crystal-amorphous mixed phase structure where crystal parts and
amorphous parts are intermingled. Note that in most cases, the
crystal part fits inside a cube whose one side is less than 100 nm.
In an image obtained with a transmission electron microscope (TEM),
a boundary between an amorphous part and a crystal part and a
boundary between crystal parts in the CAAC-OS film are not clearly
detected. Further, with the TEM, a grain boundary in the CAAC-OS
film is not clearly found. Thus, in the CAAC-OS film, a reduction
in electron mobility due to the grain boundary is suppressed.
[0109] In each of the crystal parts included in the CAAC-OS film,
for example, a c-axis is aligned in a direction parallel to a
normal vector of a surface where the CAAC-OS film is formed or a
normal vector of a surface of the CAAC-OS film. Further, in each of
the crystal parts, metal atoms are arranged in a triangular or
hexagonal configuration when seen from the direction perpendicular
to the a-b plane, and metal atoms are arranged in a layered manner
or metal atoms and oxygen atoms are arranged in a layered manner
when seen from the direction perpendicular to the c-axis. Note
that, among crystal parts, the directions of the a-axis and the
b-axis of one crystal part may be different from those of another
crystal part. In this specification, a term "perpendicular"
includes a range from 80.degree. to 100.degree., preferably from
85.degree. to 95.degree.. In addition, a term "parallel" includes a
range from -10.degree. to 10.degree., preferably from -5.degree. to
5.degree..
[0110] In the CAAC-OS film, distribution of crystal parts is not
necessarily uniform. For example, in the formation process of the
CAAC-OS film, in the case where crystal growth occurs from a
surface side of the oxide semiconductor film, the proportion of
crystal parts in the vicinity of the surface of the oxide
semiconductor film is higher than that in the vicinity of the
surface where the oxide semiconductor film is formed in some cases.
Further, when an impurity is added to the CAAC-OS film, the crystal
part in a region to which the impurity is added becomes amorphous
in some cases.
[0111] Since the c-axes of the crystal parts included in the
CAAC-OS film are aligned in the direction parallel to a normal
vector of a surface where the CAAC-OS film is formed or a normal
vector of a surface of the CAAC-OS film, the directions of the
c-axes may be different from each other depending on the shape of
the CAAC-OS film (the cross-sectional shape of the surface where
the CAAC-OS film is formed or the cross-sectional shape of the
surface of the CAAC-OS film). Note that the film deposition is
accompanied with the formation of the crystal parts or followed by
the formation of the crystal parts through crystallization
treatment such as heat treatment. Hence, the c-axes of the crystal
parts are aligned in the direction parallel to a normal vector of
the surface where the CAAC-OS film is formed or a normal vector of
the surface of the CAAC-OS film.
[0112] In a transistor using the CAAC-OS film, change in electric
characteristics due to irradiation with visible light or
ultraviolet light is small. Thus, the transistor has high
reliability.
[0113] For example, the CAAC-OS film is formed by a sputtering
method with a polycrystalline metal oxide target. By collision of
ions with the target, a crystal region included in the target may
be separated from the target along an a-b plane; in other words, a
sputtered particle having a plane parallel to an a-b plane
(flat-plate-like sputtered particle or pellet-like sputtered
particle) may flake off from the target. In that case, the
flat-plate-like sputtered particle reaches a substrate while
maintaining its crystal state, whereby the CAAC-OS film can be
formed.
[0114] For the deposition of the CAAC-OS film, the following
conditions are preferably used.
[0115] By reducing the amount of impurities entering the CAAC-OS
film during the deposition, the crystal state can be prevented from
being broken by the impurities. For example, the concentration of
impurities (e.g., hydrogen, water, carbon dioxide, or nitrogen)
which exist in the treatment chamber may be reduced. Furthermore,
the concentration of impurities in a deposition gas may be reduced.
Specifically, a deposition gas whose dew point is -80.degree. C. or
lower, preferably -100.degree. C. or lower is used.
[0116] By increasing the substrate heating temperature during the
deposition, migration of a sputtered particle is likely to occur
after the sputtered particle reaches a substrate surface.
Specifically, the substrate heating temperature during the
deposition is higher than or equal to 100.degree. C. and lower than
or equal to 740.degree. C., preferably higher than or equal to
200.degree. C. and lower than or equal to 500.degree. C. By
increasing the substrate heating temperature during the deposition,
when the flat-plate-like sputtered particle reaches the substrate,
migration occurs on the substrate surface, so that a flat plane of
the flat-plate-like sputtered particle is attached to the
substrate.
[0117] Furthermore, it is preferable that the proportion of oxygen
in the deposition gas be increased and the power be optimized in
order to reduce plasma damage at the deposition. The proportion of
oxygen in the deposition gas is 30 vol % or higher, preferably 100
vol %.
[0118] As an example of the target, an In--Gap--Zn-based oxide
target is described below.
[0119] The In--Ga--Zn-based oxide target, which is polycrystalline,
is made by mixing InO.sub.X powder, GaO.sub.Y powder, and ZnO.sub.Z
powder in a predetermined molar ratio, applying pressure, and
performing heat treatment at a temperature higher than or equal to
1000.degree. C. and lower than or equal to 1500.degree. C. Note
that X, Y, and Z are each a given positive number. Here, the
predetermined molar ratio of InO.sub.X powder to GaO.sub.Y powder
and ZnO.sub.Z powder is, for example, 2:2:1, 8:4:3, 3:1:1, 1:1:1,
4:2:3, or 3:1:2. The kinds of powder and the molar ratio for mixing
powder may be determined as appropriate depending on the desired
target.
Embodiment 2
[0120] In this embodiment, a configuration example of the memory
array 104 is described.
[0121] FIG. 8 is a block diagram illustrating a configuration
example of the memory array 104. Note that in the block diagram in
FIG. 8, circuits in the memory array 104 are classified in
accordance with their functions and separated blocks are
illustrated. However, it is difficult to classify actual circuits
according to their functions completely and it is possible for one
circuit to have a plurality of functions.
[0122] The memory array 104 illustrated in FIG. 8 includes a cell
array 160 including the plurality of memory elements 103 and a
driver circuit 161. The driver circuit 161 includes an input-output
buffer 162, a main amplifier 163, a column decoder 164, a row
decoder 165, a switch circuit 166, a precharge circuit 167, a sense
amplifier 168, and a writing circuit 169.
[0123] The input-output buffer 162 has a function of controlling
input of various signals to be used for driving the driver circuit
161 or the cell array 160 and configuration data to be written into
the cell array 160 to the memory array 104. The input-output buffer
162 also has a function of controlling output of configuration data
read out from the cell array 160 from the memory array 104.
[0124] In the case of the memory element 103 illustrated in FIG.
6A, for example, the row decoder 165 has a function of selecting
the memory elements 103 of the cell array 160 per row in accordance
with a specified address by controlling the potential supplied to
the wiring 150. The column decoder 164 has a function of performing
selection of the memory elements 103 in a column direction at the
time of writing or readout of configuration data in accordance with
a specified address by controlling the operation of the switch
circuit 166.
[0125] In the case of the memory element 103 illustrated in FIG.
6A, for example, the switch circuit 166 has a function of
establishing connection between the wiring 107 and the main
amplifier 163 and connection between the wiring 107 and the writing
circuit 169. The writing circuit 169 has a function of writing
configuration data into the memory element 103 of a specified
address via the switch circuit 166.
[0126] The sense amplifier 168 has a function of amplifying a
change in the potential of the wiring 107 at the time of reading
out configuration data from the memory element 103. The sense
amplifier 168 also has a function of temporarily storing
configuration data that is written into the memory element 103 or
configuration data that is read out from the memory element
103.
[0127] The main amplifier 163 has a function of reading out
configuration data using the potential of the wiring 107 which is
amplified by the sense amplifier 168. The precharge circuit 167 has
a function of resetting the potential of the wiring 107 before
reading out configuration data.
[0128] Note that the memory array 104 may include an address buffer
which can temporarily store the address of the specified memory
element 103.
[0129] In one embodiment of the present invention, the memory array
104 does not necessarily include the driver circuit 161; the driver
circuit 161 may be provided outside the PLD. It is also possible to
provide the driver circuit 161 in the same layer as the logic array
102 and provide the cell array 160 over the driver circuit 161 and
the logic array 102.
[0130] Next, connections between the sense amplifier 168, the
precharge circuit 167, the switch circuit 166, and the main
amplifier 163 which are assigned to the memory elements 103 of one
column are exemplified in FIG. 9. FIG. 9 illustrates one of the
memory elements 103 in FIG. 6A as an example.
[0131] The memory element 103 includes the transistor 106t, the
capacitor 111, and the capacitor 112. The memory element 103 is
connected to a wiring 107a. The sense amplifier 168, the precharge
circuit 167, and the switch circuit 166 are connected to the wiring
107a and a wiring 107b. The wirings 107a and 107b correspond to two
of the plurality of wirings 107 connected to the plurality of
memory elements 103. Note that all the memory elements 103
connected to the wirings 107a and 107b are connected to different
wirings 150.
[0132] Specifically, FIG. 9 illustrates the case where the sense
amplifier 168 is a latch sense amplifier. The sense amplifier 168
includes p-channel transistors 515 and 516 and n-channel
transistors 517 and 518. One of a source terminal and a drain
terminal of the transistor 515 is connected to a terminal SP and
the other is connected to gate electrodes of the transistors 516
and 518 and the wiring 107a. One of a source terminal and a drain
terminal of the transistor 517 is connected to the gate electrodes
of the transistors 516 and 518 and the wiring 107a and the other is
connected to a terminal SN. One of a source terminal and a drain
terminal of the transistor 516 is connected to the terminal SP and
the other is connected to gate electrodes of the transistors 515
and 517 and the wiring 107b. One of a source terminal and a drain
terminal of the transistor 518 is connected to the gate electrodes
of the transistors 515 and 517 and the wiring 107b and the other is
connected to the terminal SN.
[0133] The precharge circuit 167 includes n-channel transistors 519
to 521. The transistors 519 to 521 may be p-channel transistors.
One of a source terminal and a drain terminal of the transistor 519
is connected to the wiring 107a and the other is connected to a
terminal Pre. One of a source terminal and a drain terminal of the
transistor 520 is connected to the wiring 107b and the other is
connected to the terminal Pre. One of a source terminal and a drain
terminal of the transistor 521 is connected to the wiring 107a and
the other is connected to the wiring 107b. Gate electrodes of the
transistors 519 to 521 are connected to a wiring PL.
[0134] The switch circuit 166 includes n-channel transistors 522
and 523. The transistors 522 and 523 may be p-channel transistors.
One of a source terminal and a drain terminal of the transistor 522
is connected to the wiring 107a and the other is connected to a
wiring IOa. One of a source terminal and a drain terminal of the
transistor 523 is connected to the wiring 107b and the other is
connected to a wiring IOb. Gate electrodes of the transistors 522
and 523 are connected to a terminal CSL. The potential of the
terminal CSL is controlled by the column decoder 164.
[0135] The wirings IOa and IOb are connected to the main amplifier
163. The writing circuit 169 has a function of supplying potential
to the wirings IOa and IOb in accordance with configuration
data.
[0136] The sense amplifier 168 is not limited to the above latch
sense amplifier, and may be a current-mirror sense amplifier or a
single-end sense amplifier. In the case where the sense amplifier
168 is a single-end sense amplifier, the potential of the wiring
107b need not be reset; thus, the transistors 520 and 521 in the
precharge circuit 167 can be omitted.
[0137] The combination of the wirings 107a and 107b can be
determined as appropriate in accordance with an array structure. In
one embodiment of the present invention, an array structure such as
a folded bit line structure, a cross-point structure, or an open
bit line structure can be used, and two of the plurality of wirings
107 connected to the plurality of memory elements 103 are connected
to the main amplifier 163 and the switch circuit 166 in accordance
with the array structure. Note that as mentioned above, all the
memory elements 103 connected to the wirings 107a and 107b are
connected to different wirings 150.
[0138] Next, an example of the operation of the memory element 103,
the sense amplifier 168, the precharge circuit 167, the switch
circuit 166, and the main amplifier 163 illustrated in FIG. 9 at
the time of reading out configuration data is described with
reference to a timing chart shown in FIG. 10.
[0139] First, in a period T1, the transistors 519 to 521 included
in the precharge circuit 167 are turned on and the potentials of
the wirings 107a and 107b are reset. Specifically, in this
embodiment, a high-level potential VH_PL is supplied to the wiring
PL, so that the transistors 519 to 521 in the precharge circuit 167
are turned on. In this manner, a potential Vpre of the terminal Pre
is supplied to the wirings 107a and 107b.
[0140] Note that in the period T1, a low-level potential VL_CSL is
supplied to the terminal CSL; thus, the transistors 522 and 523 in
the switch circuit 166 are in an off state. Further, a low-level
potential VL WL is supplied to the wiring 150 (correspond to WL in
FIG. 10); thus, the transistor 106t in the memory element 103 is in
an off state. The potential Vpre is supplied to the terminal SP and
the terminal SN; thus, the sense amplifier 168 is in an off
state.
[0141] Then, a low-level potential VL_PL is supplied to the wiring
PL, so that the transistors 519 to 521 in the precharge circuit 167
are turned off. In a period T2, the wiring 150 is selected.
Specifically, in this embodiment, a high-level potential VH_WL is
supplied to the wiring 150, so that the wiring 150 is selected and
the transistor 106t in the memory element 103 is turned on. In this
manner, the capacitors 111 and 112 are connected to the wiring 107a
through the transistor 106t. When the capacitors 111 and 112 are
electrically connected to the wiring 107a, the potential of the
wiring 107a changes depending on the amount of charge held in the
capacitors 111 and 112.
[0142] The timing chart in FIG. 10 shows, as an example, the case
where the amount of charge accumulated in the capacitors 111 and
112 is large. Specifically, when the amount of charge accumulated
in the capacitors 111 and 112 is large, charge is released to the
wiring 107a from the capacitors 111 and 112, so that the potential
of the wiring 107a rises from the potential Vpre by .DELTA.V1. On
the other hand, when the amount of charge accumulated in the
capacitors 111 and 112 is small, charge flows into the capacitors
111 and 112 from the wiring 107a, so that the potential of the
wiring 107a falls from the potential Vpre by .DELTA.V2.
[0143] In the period T2, the low-level potential VL_CSL is still
supplied to the terminal CSL; thus, the transistors 522 and 523 in
the switch circuit 166 remain in an off state. Further, the
potential Vpre is still supplied to the terminal SP and the
terminal SN; thus, the sense amplifier 168 remains in an off
state.
[0144] Next, in a period T3, a high-level potential VH_SP is
supplied to the terminal SP and a low-level potential VL_SN is
supplied to the terminal SN, so that the sense amplifier 168 is
turned on. The sense amplifier 168 has a function of amplifying the
potential difference between the wirings 107a and 107b (.DELTA.V1
in FIG. 10). Accordingly, in the case of the timing chart in FIG.
10, when the sense amplifier 168 is turned on, the potential of the
wiring 107a rises from the potential Vpre.sub.+.DELTA.V1 to
approach the potential VH_SP of the terminal SP. In addition, the
potential of the wiring 107b falls from the potential Vpre to
approach the potential VL_SN of the terminal SN.
[0145] Note that in the case where the potential of the wiring 107a
is Vpre-.DELTA.V2 at the beginning of the period T3, when the sense
amplifier 168 is turned on, the potential of the wiring 107a falls
from the potential Vpre-.DELTA.V2 to approach the potential VL_SN
of the terminal SN. In addition, the potential of the wiring 107b
rises from the potential Vpre to approach the potential VH_SP of
the terminal SP.
[0146] In the period T3, the low-level potential VL_PL is still
supplied to the wiring PL, so that the transistors 519 to 521 in
the precharge circuit 167 remain in an off state. Further, the
low-level potential VL_CSL is still supplied to the terminal CSL;
thus, the transistors 522 and 523 in the switch circuit 166 remain
in an off state. The high-level potential VH WL is still supplied
to the wiring 150; thus, the transistor 106t in the memory element
103 remains in an on state.
[0147] Next, in a period T4, the switch circuit 166 is turned on by
control of the potential supplied to the terminal CSL.
Specifically, in this embodiment, a high-level potential VH CSL is
supplied to the terminal CSL, so that the transistors 522 and 523
in the switch circuit 166 are turned on. In this manner, the
potential of the wiring 107a and the potential of the wiring 107b
are supplied to the main amplifier 163 through the wirings IOa and
IOb. The level of a potential Vout that is output from the main
amplifier 163 differs depending on whether the potential of the
wiring IOa is high or low compared with the potential of the wiring
IOb. This means that a signal including the potential Vout includes
configuration data.
[0148] In the period T4, the low-level potential VL_PL is still
supplied to the wiring PL, so that the transistors 519 to 521 in
the precharge circuit 167 remain in an off state. The high-level
potential VH WL is still supplied to the wiring 150; thus, the
transistor 106t in the memory element 103 remains in an on state.
The high-level potential VH_SP is still supplied to the terminal SP
and the low-level potential VL_SN is still supplied to the terminal
SN; thus, the sense amplifier 168 remains in an on state.
[0149] When the period T4 ends, the switch circuit 166 is turned
off by control of the potential supplied to the terminal CSL.
Specifically, in this embodiment, the low-level potential VL_CSL is
supplied to the terminal CSL, so that the transistors 522 and 523
in the switch circuit 166 are turned off In addition, the selection
of the wiring 150 is terminated. Specifically, in this embodiment,
the low-level potential VL_WL is supplied to the wiring 150, so
that the wiring 150 is deselected and the transistor 106t in the
memory element 103 is turned off
[0150] Configuration data is read out from the memory element 103
by the above operation through the periods T1 to T4.
[0151] In the case where the read out configuration data is written
into the memory element 103 again, the sense amplifier 168 is kept
in an on state after the configuration data is read out until
writing of the configuration data is performed again. In this
manner, the potentials of the wirings 107a and 107b are held by the
sense amplifier 168 even after the configuration data is read out.
The transistors 522 and 523 in the switch circuit 166 are turned
off after the configuration data is read out. Then, the wiring 150
is selected and the transistor 106t is turned on, so that the
capacitors 111 and 112 are connected to the wiring 107a. Charge is
accumulated in the capacitors 111 and 112 in accordance with the
potential of the wiring 107a, whereby the read out configuration
data is written into the memory element 103 again.
[0152] In the case where new configuration data is written into the
memory element 103 from the writing circuit 169, first, the
high-level potential VH_SP is supplied to the terminal SP and the
low-level potential VL_SN is supplied to the terminal SN, so that
the sense amplifier 168 is turned on. Then, the potentials of the
wirings IOa and IOb are set to levels corresponding to the
configuration data under the control of the writing circuit 169,
and the transistors 522 and 523 in the switch circuit 166 are
turned on. In this manner, the potential of the wiring IOa is
supplied to the wiring 107a, and the potential of the wiring IOb is
supplied to the wiring 107b. Then, the wiring 150 is selected and
the transistor 106t is turned on, so that the capacitors 111 and
112 are connected to the wiring 107a. Charge is accumulated in the
capacitors 111 and 112 in accordance with the potential of the
wiring 107a, whereby the configuration data is written into the
memory element 103.
[0153] Note that after the potential of the wiring IOa is supplied
to the wiring 107a and the potential of the wiring IOb is supplied
to the wiring 107b, the relation in level between the potential of
the wiring 107a and the potential of the wiring 107b is kept by the
sense amplifier 168 as long as the sense amplifier is in an on
state even after the transistors 522 and 523 in the switch circuit
166 are turned of Therefore, the timing of switching the
transistors 522 and 523 from an on state to an off state in the
switch circuit 166 may be either before or after the selection of
the wiring 150.
[0154] This embodiment can be implemented in appropriate
combination with any of the other embodiments.
Embodiment 3
[0155] In this embodiment, a configuration example of the LUT 113
included in the PLE 101 is described. The LUT 113 can be composed
of a plurality of multiplexers. Configuration data 105 can be input
to any of input terminals and control terminals of the plurality of
multiplexers.
[0156] FIG. 11A illustrates one mode of the LUT 113 included in the
PLE 101.
[0157] In FIG. 11A, the LUT 113 is composed of seven two-input
multiplexers (a multiplexer 31, a multiplexer 32, a multiplexer 33,
a multiplexer 34, a multiplexer 35, a multiplexer 36, and a
multiplexer 37). Input terminals of the multiplexers 31 to 34
correspond to input terminals Ml to M8 of the LUT 113.
[0158] Control terminals of the multiplexers 31 to 34 are
electrically connected to each other and correspond to an input
terminal IN3 of the LUT 113. Output terminals of the multiplexers
31 and 32 are electrically connected to two input terminals of the
multiplexer 35. Output terminals of the multiplexers 33 and 34 are
electrically connected to two input terminals of the multiplexer
36. Control terminals of the multiplexers 35 and 36 are
electrically connected to each other and correspond to an input
terminal IN2 of the LUT 113. Output terminals of the multiplexers
35 and 36 are electrically connected to two input terminals of the
multiplexer 37. A control terminal of the multiplexer 37
corresponds to an input terminal IN1 of the LUT 113. An output
terminal of the multiplexer 37 corresponds to an output terminal
OUT of the LUT 113.
[0159] When configuration data 105 is input from the memory element
103 to the input terminals M1 to M8, the kind of logic operation
performed by the LUT 113 can be determined.
[0160] For example, in the case where configuration data 105
(digital values "0", "1", "0", "1", "0", "1", "1", and "1") is
input to the input terminals M1 to M8 of the LUT 113 in FIG. 11A,
the function of an equivalent circuit in FIG. 11C can be
obtained.
[0161] FIG. 11B illustrates another mode of the LUT 113 included in
the PLE 101.
[0162] In FIG. 11B, the LUT 113 is composed of three two-input
multiplexers (a multiplexer 41, a multiplexer 42, and a multiplexer
43) and a two-input OR circuit 44.
[0163] Output terminals of the multiplexers 41 and 42 are
electrically connected to two input terminals of the multiplexer
43. An output terminal of the OR circuit 44 is electrically
connected to a control terminal of the multiplexer 43. An output
terminal of the multiplexer 43 corresponds to the output terminal
OUT of the LUT 113.
[0164] When configuration data 105 is input from the memory element
103 to any of a control terminal A1, an input terminal A2, and an
input terminal A3 of the multiplexer 41, a control terminal A6, an
input terminal A4, and an input terminal A5 of the multiplexer 42,
and an input terminal A7 and an input terminal A8 of the OR circuit
44, the kind of logic operation performed by the LUT 113 can be
determined.
[0165] For example, in the case where configuration data 105
(digital values "0", "1", "0", "0", and "0") is input to the input
terminal A2, the input terminal A4, the input terminal A5, the
control terminal A6, and the input terminal A8 of the LUT 113 from
the memory elements 103 in FIG. 11B, the function of the equivalent
circuit in FIG. 11C can be obtained. In the above configuration,
the control terminal A1, the input terminal A3, and the input
terminal A7 correspond to the input terminal IN1, the input
terminal IN2, and the input terminal IN3, respectively.
[0166] Note that FIGS. 11A and 11B each illustrate an example of
the LUT 113 composed of two-input multiplexers; however, the LUT
113 may be composed of multiplexers with three or more inputs.
[0167] The LUT 113 may further include any of or all of a diode, a
resistor, a logic circuit (or a logic element), and a switch in
addition to the multiplexers. As the logic circuit (or the logic
element), a buffer, an inverter, a NAND circuit, a NOR circuit, a
three-state buffer, a clocked inverter, or the like can be used. As
the switch, an analog switch, a transistor, or the like can be
used, for example.
[0168] Although the case where three-input and one-output logic
operation as illustrated in FIG. 11C is performed using the LUT 113
illustrated in FIG. 11A or FIG. 11B is described, this embodiment
is not limited thereto. When the LUT 113 and configuration data 105
to be input are determined as appropriate, logic operation with
four or more inputs and two or more outputs can be performed.
[0169] This embodiment can be implemented in appropriate
combination with any of the other embodiments.
Embodiment 4
[0170] In this embodiment, a method for manufacturing a PLD and a
method for manufacturing a semiconductor device will be described
by giving an example in which an oxide semiconductor is used for an
active layer of the transistor 106t in the memory element 103
illustrated in FIG. 6A and silicon is used for an active layer of a
transistor 230 included in a programmable logic element.
[0171] Besides silicon, a semiconductor material such as germanium,
silicon germanium, or single crystal silicon carbide may be used
for the transistor 230 included in the programmable logic element.
For example, the transistor including silicon can be formed using a
single crystal semiconductor substrate such as a silicon wafer, a
silicon thin film which is formed by an SOI method, a silicon thin
film which is formed by a vapor deposition method, or the like.
[0172] In this embodiment, first, as illustrated in FIG. 12A, an
insulating film 701 and a single crystal semiconductor film 702 are
formed over a substrate 700.
[0173] Although there is no particular limitation on a material
which can be used as the substrate 700, it is necessary that the
material have at least heat resistance high enough to withstand
heat treatment to be performed later. For example, a glass
substrate formed by a fusion process or a float process, a quartz
substrate, a semiconductor substrate, a ceramic substrate, or the
like can be used as the substrate 700. As the glass substrate, in
the case where the temperature of heat treatment to be performed
later is high, a glass substrate having a strain point of
730.degree. C. or higher is preferably used.
[0174] In this embodiment, a method for manufacturing the
transistor included in the programmable logic element is described
by giving an example in which the semiconductor film 702 is formed
using single crystal silicon. Note that a specific example of a
method for forming the single crystal semiconductor film 702 is
briefly described. First, an ion beam including ions which are
accelerated by an electric field enters a bond substrate which is
the single crystal semiconductor substrate and a fragile layer
which is fragile because of local disorder of the crystal structure
is formed in a region at a certain depth from a surface of the bond
substrate. The depth at which the fragile layer is formed can be
adjusted by the acceleration energy of the ion beam and the angle
at which the ion beam enters. Then, the bond substrate and the
substrate 700 which is provided with the insulating film 701 are
attached to each other so that the insulating film 701 is
sandwiched therebetween. After the bond substrate and the substrate
700 overlap with each other, a pressure of approximately 1
N/cm.sup.2 to 500 N/cm.sup.2, preferably 11 N/cm.sup.2 to 20
N/cm.sup.2 is applied to part of the bond substrate and part of the
substrate 700 so that the substrates are attached to each other.
When the pressure is applied, bonding between the bond substrate
and the insulating film 701 starts from the parts, which results in
bonding of the entire surface where the bond substrate and the
insulating film 701 are in close contact with each other.
Subsequently, heat treatment is performed, so that microvoids that
exist in the fragile layer are combined and the microvoids increase
in volume. Accordingly, a single crystal semiconductor film which
is part of the bond substrate is separated from the bond substrate
along the fragile layer. The heat treatment is performed at a
temperature not exceeding the strain point of the substrate 700.
Then, the single crystal semiconductor film is processed into a
desired shape by etching or the like, so that the semiconductor
film 702 can be formed.
[0175] In order to control the threshold voltage, an impurity
element imparting p-type conductivity, such as boron, aluminum, or
gallium, or an impurity element imparting n-type conductivity, such
as phosphorus or arsenic, may be added to the semiconductor film
702. An impurity element for controlling the threshold voltage may
be added to the semiconductor film which is not patterned or may be
added to the patterned semiconductor film 702. Alternatively, the
impurity element for controlling the threshold voltage may be added
to the bond substrate. Further alternatively, the impurity element
may be added to the bond substrate in order to roughly control the
threshold voltage, and the impurity element may be further added to
the semiconductor film which is not patterned or the patterned
semiconductor film 702 in order to finely control the threshold
voltage.
[0176] Note that although an example in which a single crystal
semiconductor film is used is described in this embodiment, the
present invention is not limited to this structure. For example, a
polycrystalline, microcrystalline, or amorphous semiconductor film
which is formed over the insulating film 701 by vapor deposition
may be used. Alternatively, the semiconductor film may be
crystallized by a known technique. As the known technique of
crystallization, a laser crystallization method using a laser beam
and a crystallization method using a catalytic element are given.
Alternatively, a crystallization method using a catalytic element
and a laser crystallization method may be combined. When a
heat-resistant substrate such as a quartz substrate is used, any of
a thermal crystallization method using an electrically heated
furnace, a lamp annealing crystallization method using infrared
light, a crystallization method using a catalytic element, and a
crystallization method using a high-temperature annealing method at
approximately 950.degree. C. may be used.
[0177] Next, as illustrated in FIG. 12B, a gate insulating film 703
is formed over the semiconductor film 702. Then, a gate electrode
704 is formed over the gate insulating film 703.
[0178] The gate insulating film 703 can be formed by oxidation or
nitridation of a surface of the semiconductor film 702 by
high-density plasma treatment, heat treatment, or the like. The
high-density plasma treatment is performed, for example, by using a
mixed gas of a rare gas such as He, Ar, Kr, or Xe, and oxygen,
nitrogen oxide, ammonia, nitrogen, hydrogen, or the like. In this
case, by exciting plasma by introduction of microwaves, plasma with
a low electron temperature and high density can be generated. By
oxidation or nitridation of the surface of the semiconductor film
with oxygen radicals (including OH radicals in some cases) or
nitrogen radicals (including NH radicals in some cases) generated
by such high-density plasma, an insulating film with a thickness of
1 nm to 20 nm, preferably 5 nm to 10 nm can be formed to be in
contact with the semiconductor film. For example, a surface of the
semiconductor film 702 is oxidized or nitrided using nitrous oxide
(N.sub.2O) diluted with Ar by 1 time to 3 times (flow rate ratio)
by application of a microwave (2.45 GHz) power of 3 kW to 5 kW at a
pressure of 10 Pa to 30 Pa. By this treatment, an insulating film
having a thickness of 1 nm to 10 nm (preferably 2 nm to 6 nm) is
formed. Further, nitrous oxide (N.sub.2O) and silane (SiH.sub.4)
are introduced and a microwave (2.45 GHz) power of 3 kW to 5 kW is
applied at a pressure of 10 Pa to 30 Pa so that a silicon
oxynitride film is formed by a vapor deposition method, thereby
forming the gate insulating film. With a combination of a
solid-phase reaction and a reaction by a vapor deposition method,
the gate insulating film with low interface state density and
excellent withstand voltage can be formed.
[0179] The oxidation or nitridation of the semiconductor film by
the high-density plasma treatment proceeds by solid-phase reaction.
Thus, interface state density between the gate insulating film 703
and the semiconductor film 702 can be extremely low. Further, by
direct oxidation or nitridation of the semiconductor film 702 by
high-density plasma treatment, variation in the thickness of the
insulating film to be formed can be suppressed. Moreover, in the
case where the semiconductor film has crystallinity, the surface of
the semiconductor film is oxidized with solid reaction by the high-
density plasma treatment to restrain fast oxidation only in a
crystal grain boundary; therefore, the gate insulating film with
uniformity and low interface state density can be formed.
Variations in the characteristics of a transistor whose gate
insulating film partly or entirely includes an insulating film
formed by high-density plasma treatment can be suppressed.
[0180] The gate insulating film 703 may be formed as a single layer
or a stack of layers containing any of silicon oxide, silicon
nitride oxide, silicon oxynitride, silicon nitride, hafnium oxide,
aluminum oxide, tantalum oxide, yttrium oxide, hafnium silicate
(HfSi.sub.xO.sub.y, (x>0, y>0)), hafnium silicate
(HfSi.sub.xO.sub.y(x>0, y>0)) to which nitrogen is added,
hafnium aluminate (HfAl.sub.xO.sub.y, (x>0, y>0)) to which
nitrogen is added, and the like by a plasma CVD method, a
sputtering method, or the like.
[0181] Note that in this specification, an oxynitride is a
substance which includes more oxygen than nitrogen, and a nitride
oxide is a substance which includes more nitrogen than oxygen.
[0182] The thickness of the gate insulating film 703 may be, for
example, greater than or equal to 1 nm and less than or equal to
100 nm, preferably greater than or equal to 10 nm and less than or
equal to 50 nm. In this embodiment, a single-layer insulating film
containing silicon oxynitride with a thickness of about 20 nm
formed by a plasma CVD method is used as the gate insulating film
703.
[0183] A conductive film is formed so as to cover the gate
insulating film 703 and then is processed (patterned) into a
predetermined shape, so that the gate electrode 704 can be formed.
The conductive film can be formed by a CVD method, a sputtering
method, a vapor deposition method, a spin coating method, or the
like. For the conductive film, tantalum (Ta), tungsten (W),
titanium (Ti), molybdenum (Mo), aluminum (Al), copper (Cu),
chromium (Cr), niobium (Nb), or the like can be used. Moreover, an
alloy containing the above metal as the main component or a
compound containing the above metal may be used. Alternatively, the
conductive film may be formed using a semiconductor such as
polycrystalline silicon doped with an impurity element such as
phosphorus which imparts conductivity to the semiconductor
film.
[0184] Note that the gate electrode 704 may be formed using a
single-layer conductive film or a stack of a plurality of
conductive films.
[0185] As a combination of two conductive films, tantalum nitride
or tantalum can be used for a first conductive film and tungsten
can be used for a second conductive film. Besides, the following
combinations are given: tungsten nitride and tungsten, molybdenum
nitride and molybdenum, aluminum and tantalum, aluminum and
titanium, and the like. Since tungsten and tantalum nitride have
high heat resistance, heat treatment for thermal activation can be
performed after the two conductive films are formed. Alternatively,
as the combination of the two conductive films, for example, nickel
silicide and silicon doped with an impurity element which imparts
n-type conductivity, tungsten silicide and silicon doped with an
impurity element which imparts n-type conductivity, or the like can
be used.
[0186] In the case of employing a three-layer structure in which
three conductive films are stacked, a stacked-layer structure of a
molybdenum film, an aluminum film, and a molybdenum film is
preferable.
[0187] Further, a light-transmitting oxide conductive film of
indium oxide, a mixture of indium oxide and tin oxide, a mixture of
indium oxide and zinc oxide, zinc oxide, zinc aluminum oxide, zinc
aluminum oxynitride, zinc gallium oxide, or the like can also be
used as the gate electrode 704.
[0188] In this embodiment, the gate electrode 704 in which tungsten
with a thickness of about 170 nm is stacked over tantalum nitride
with a thickness of about 30 nm is used.
[0189] Alternatively, the gate electrode 704 may be selectively
formed by a droplet discharge method without the use of a mask. A
droplet discharge method is a method for forming a predetermined
pattern by discharge or ejection of a droplet containing a
predetermined composition from an orifice, and includes an inkjet
method in its category.
[0190] In addition, the gate electrode 704 can be formed in such a
manner that a conductive film is formed and then is etched by
inductively coupled plasma (ICP) etching under appropriately
controlled conditions (e.g., the amount of electric power applied
to a coiled electrode layer, the amount of electric power applied
to an electrode layer on the substrate side, and the electrode
temperature on the substrate side) to have a desired tapered shape.
Further, an angle and the like of the tapered shape may be
controlled by the shape of a mask. Note that as an etching gas, a
chlorine- based gas such as chlorine, boron chloride, silicon
chloride, or carbon tetrachloride; a fluorine-based gas such as
carbon tetrafluoride, sulfur fluoride, or nitrogen fluoride; or
oxygen can be used as appropriate.
[0191] Next, an impurity element imparting one conductivity type is
added to the semiconductor film 702 with the use of the gate
electrode 704 as a mask, whereby a channel formation region 705
which overlaps with the gate electrode 704 and a pair of impurity
regions 706 between which the channel formation region 705 is
sandwiched are formed in the semiconductor film 702 as illustrated
in FIG. 12C.
[0192] In this embodiment, the case where an impurity element which
imparts n-type conductivity (e.g., phosphorus) is added to the
semiconductor film 702 is described.
[0193] Next, as illustrated in FIG. 12D, an insulating film 707, an
insulating film 708, and an insulating film 709 are formed to cover
the gate insulating film 703 and the gate electrode 704.
Specifically, an inorganic insulating film of silicon oxide,
silicon nitride, silicon nitride oxide, silicon oxynitride,
aluminum nitride, aluminum nitride oxide, or the like can be used
as the insulating film 707, the insulating film 708, and the
insulating film 709. In particular, the insulating film 707, the
insulating film 708, and the insulating film 709 are preferably
formed using a low dielectric constant (low-k) material because
capacitance due to overlapping of electrodes or wirings can be
sufficiently reduced. Note that a porous insulating film containing
any of the above materials may be employed as the insulating film
707, the insulating film 708, and the insulating film 709. Since
the porous insulating film has lower dielectric constant than a
dense insulating film, parasitic capacitance due to electrodes or
wirings can be further reduced.
[0194] In this embodiment, an example in which a 50-nm-thick
silicon oxynitride film is used as the insulating film 707, a
100-nm-thick silicon nitride oxide film is used as the insulating
film 708, and a 450-nm-thick silicon oxynitride film is used as the
insulating film 709 is described. In addition, although an example
in which the insulating film 707, the insulating film 708, and the
insulating film 709 are formed over the gate electrode 704 is
described in this embodiment, only one insulating film or a stack
of two insulating films or four or more insulating films may be
formed over the gate electrode 704.
[0195] Next, as illustrated in FIG. 13A, openings are formed in the
gate insulating film 703, the insulating film 707, the insulating
film 708, and, the insulating film 709 by etching or the like in
order to expose part of the pair of the impurity regions 706 and
part of the gate electrode 704; then, a conductive film 710 and a
conductive film 711 which are in contact with the pair of the
impurity regions 706 and a conductive film 712 which is in contact
with the gate electrode 704 are formed. In addition, an insulating
film 713 is formed over the insulating film 709 so as to cover the
conductive films 710 to 712.
[0196] A conductive film which is to be the conductive films 710 to
712 can be formed using any of the following materials: an element
selected from aluminum, chromium, copper, tantalum, titanium,
molybdenum, and tungsten; an alloy containing any of these elements
as a component; an alloy film containing any of these elements in
combination; and the like. Alternatively, the conductive film may
have a structure in which a film of a refractory metal such as
chromium, tantalum, titanium, molybdenum, or tungsten is stacked
over or below a metal film of aluminum, copper, or the like.
Aluminum or copper is preferably used in combination with a
refractory metal material in order to avoid problems with heat
resistance and corrosion. As the refractory metal material,
molybdenum, titanium, chromium, tantalum, tungsten, neodymium,
scandium, yttrium, or the like can be used.
[0197] Further, the conductive film which is to be the conductive
films 710 to 712 may have a single-layer structure or a
stacked-layer structure of two or more layers. For example, a
single-layer structure of an aluminum film containing silicon, a
two-layer structure in which a titanium film is stacked over an
aluminum film, a three-layer structure in which a titanium film, an
aluminum film, and a titanium film are stacked in that order, and
the like can be given.
[0198] For the conductive film which is to be the conductive films
710 to 712, a conductive metal oxide may be used. As the conductive
metal oxide, indium oxide, tin oxide, zinc oxide, a mixture of
indium oxide and tin oxide, a mixture of indium oxide and zinc
oxide, or the conductive metal oxide material to which silicon or
silicon oxide is added can be used.
[0199] In this embodiment, a conductive film in which a titanium
film with a thickness of about 50 nm, an aluminum film with a
thickness of about 200 nm, and a titanium film with a thickness of
about 100 nm are stacked is used for the conductive films 710 to
712.
[0200] The insulating film 713 may have either a single-layer
structure or a stacked-layer structure of two or more layers, and
preferably has a highly planar surface. As the insulating film 713,
silicon oxide, silicon nitride, silicon oxynitride, or silicon
nitride oxide can be used, for example. The insulating film 713 can
be formed by a CVD method such as a plasma CVD method, a photo CVD
method, or a thermal CVD method.
[0201] Further, as the insulating film 713, a silicon oxide film
formed by chemical vapor deposition using organosilane can be used.
For organosilane, tetraethoxysilane (TEOS) (chemical formula:
Si(OC.sub.2H.sub.5).sub.4), trimethylsilane (TMS) (chemical
formula: (CH.sub.3).sub.3SiH), tetramethylcyclotetrasiloxane
(TMCTS), octamethylcyclotetrasiloxane (OMCTS), hexamethyldisilazane
(HMDS), triethoxysilane (chemical formula:
SiH(OC.sub.2H.sub.5).sub.3), tris(dimethylamino)silane (chemical
formula: SiH(N(CH.sub.3).sub.2).sub.3), or the like can be used. It
is needless to say that silicon oxide, silicon oxynitride, silicon
nitride, silicon nitride oxide, or the like may be formed using
inorganic silane such as monosilane, disilane, or trisilane.
[0202] In this embodiment, the insulating film 713 having a
thickness of about 1.5 .mu.m and containing silicon oxide is formed
using TEOS.
[0203] Through the above process, the transistor 230 included in
the programmable logic element can be formed. The transistor 230
includes the semiconductor film 702, the gate insulating film 703
over the semiconductor film 702, the gate electrode 704 formed to
overlap with the semiconductor film 702 over the gate insulating
film 703, and the conductive film 710 and the conductive film 711
which function as a source electrode and a drain electrode and are
connected to the impurity regions 706 included in the semiconductor
film 702.
[0204] Next, as illustrated in FIG. 13B, the insulating film 713 is
subjected to CMP (chemical mechanical polishing) or etching, so
that a surface of the conductive film 712 is exposed. Note that in
order to improve the characteristics of the transistor 106t which
is formed later, a surface of the insulating film 713 is preferably
planarized as much as possible.
[0205] Next, a method for manufacturing the transistor 106t is
described. First, as illustrated in FIG. 13C, an insulating film
714 is formed over the insulating film 713 and the conductive film
712, and then an oxide semiconductor film 715 is formed over the
insulating film 714.
[0206] The insulating film 714 can be formed with the use of a
material similar to those of the insulating films 707 to 709. In
this embodiment, a silicon oxynitride film having a thickness of
about 300 nm is used as the insulating film 714.
[0207] The oxide semiconductor film 715 can be formed by processing
an oxide semiconductor film formed over the insulating film 714
into a desired shape. The thickness of the oxide semiconductor film
is greater than or equal to 2 nm and less than or equal to 200 nm,
preferably greater than or equal to 3 nm and less than or equal to
50 nm, more preferably greater than or equal to 3 nm and less than
or equal to 20 nm. The oxide semiconductor film is formed by a
sputtering method using an oxide semiconductor target. The oxide
semiconductor film can be formed by a sputtering method in a rare
gas (e.g., argon) atmosphere, an oxygen atmosphere, or a mixed
atmosphere of a rare gas (e.g., argon) and oxygen.
[0208] Note that before the oxide semiconductor film is formed by a
sputtering method, dust attached to a surface of the insulating
film 714 is preferably removed by reverse sputtering in which an
argon gas is introduced and plasma is generated. The reverse
sputtering refers to a method in which voltage is applied to a
substrate side, but not to a target side, in an argon atmosphere by
using an RF power source and plasma is generated in the vicinity of
the substrate to modify a surface. Note that instead of an argon
atmosphere, a nitrogen atmosphere, a helium atmosphere, or the like
may be used. Alternatively, an argon atmosphere to which oxygen,
nitrous oxide, or the like is added may be used. Alternatively, an
argon atmosphere to which chlorine, carbon tetrafluoride, or the
like is added may be used.
[0209] As the oxide semiconductor, for example, any of the
following can be used: indium oxide; tin oxide; zinc oxide; a
two-component metal oxide such as an In--Zn-based oxide, a
Sn--Zn-based oxide, an Al--Zn-based oxide, a Zn--Mg-based oxide, a
Sn--Mg-based oxide, an In--Mg-based oxide, or an In--Ga-based
oxide; a three-component metal oxide such as an In--Gap--Zn-based
oxide (also referred to as IGZO), an In--Al--Zn-based oxide, an
In--Sn--Zn-based oxide, a Sn--Ga--Zn-based oxide, an
Al--Ga--Zn-based oxide, a Sn--Al--Zn-based oxide, an
In--Hf--Zn-based oxide, an In--La--Zn-based oxide, an
In--Pr--Zn-based oxide, an In--Nd--Zn-based oxide, an
In--Sm--Zn-based oxide, an In--Eu--Zn-based oxide, an
In--Gd--Zn-based oxide, an In--Tb--Zn-based oxide, an
In--Dy--Zn-based oxide, an In--Ho--Zn-based oxide, an
In--Er--Zn-based oxide, an In--Tm--Zn-based oxide, an
In--Yb--Zn-based oxide, or an In--Lu--Zn-based oxide; a
four-component metal oxide such as an In--Sn--Ga--Zn-based oxide,
an In--Hf--Ga--Zn-based oxide, an In--Al--Ga--Zn-based oxide, an
In--Sn--Al--Zn-based oxide, an In--Sn--Hf--Zn-based oxide, or an
In--Hf--Al--Zn-based oxide.
[0210] In this embodiment, an In--Gap--Zn-based oxide semiconductor
thin film with a thickness of 30 nm, which is obtained by a
sputtering method using a target including indium (In), gallium
(Ga), and zinc (Zn), is used as the oxide semiconductor film. As
the above target, it is preferable to use a target having an atomic
ratio of In:Ga:Zn=1:1:1, 4:2:3, 3:1:2, 1:1:2, 2:1:3, or 3:1:4. The
filling rate of the target including In, Ga, and Zn is higher than
or equal to 90% and lower than or equal to 100%, preferably higher
than or equal to 95% and lower than 100%. With the use of the
target with high filling rate, a dense oxide semiconductor film is
formed.
[0211] In the case where an In--Zn-based material is used for the
oxide semiconductor film, the atomic ratio of metal elements in a
target to be used is In:Zn=50:1 to 1:2 (In.sub.2O.sub.3:ZnO=25:1 to
1:4 in a molar ratio), preferably In:Zn=20:1 to 1:1
(In.sub.2O.sub.3:ZnO=10:1 to 1:2 in a molar ratio), further
preferably In:Zn=15:1 to 1.5:1 (In.sub.2O.sub.3:ZnO=15:2 to 3:4 in
a molar ratio). For example, in a target used for forming an
In--Zn-based oxide semiconductor with an atomic ratio of
In:Zn:O=X:Y:Z, the relation of Z>1.5X+Y is satisfied. The
mobility can be improved by keeping the ratio of Zn within the
above range.
[0212] In the case of forming an In--Sn--Zn-based oxide
semiconductor film as the oxide semiconductor film by a sputtering
method, an In--Sn--Zn-based oxide target in which the atomic ratio
of metal elements, In, Sn, and Zn is 1:1:1, 2:1:3, 1:2:2, or 4:9:7
is used.
[0213] In this embodiment, the oxide semiconductor film is formed
in such a manner that the substrate is held in a treatment chamber
kept in a reduced pressure state, moisture remaining in the
treatment chamber is removed, a sputtering gas from which hydrogen
and moisture are removed is introduced, and the target is used. The
substrate temperature may be higher than or equal to 100.degree. C.
and lower than or equal to 600.degree. C., preferably higher than
or equal to 200.degree. C. and lower than or equal to 400.degree.
C. in film formation. By formation of the oxide semiconductor film
in a state where the substrate is heated, the concentration of
impurities included in the formed oxide semiconductor film can be
reduced. In addition, damage by sputtering can be reduced. In order
to remove moisture remaining in the treatment chamber, an
entrapment vacuum pump is preferably used. For example, a cryopump,
an ion pump, or a titanium sublimation pump is preferably used. The
evacuation unit may be a turbo pump provided with a cold trap. In
the treatment chamber which is evacuated with the cryopump, for
example, a hydrogen atom, a compound containing a hydrogen atom,
such as water (H.sub.2O), (more preferably, also a compound
containing a carbon atom), and the like are removed, whereby the
impurity concentration in the oxide semiconductor film formed in
the treatment chamber can be reduced.
[0214] One example of the film formation condition is as follows:
the distance between the substrate and the target is 100 mm, the
pressure is 0.6 Pa, the power of the direct-current (DC) power
source is 0.5 kW, and the atmosphere is an oxygen atmosphere (the
proportion of the oxygen flow rate is 100%) %). Note that a pulsed
direct-current (DC) power source is preferable because dust
generated in film formation can be reduced and the film thickness
can be made uniform.
[0215] Moreover, when the leakage rate of the treatment chamber of
the sputtering apparatus is set lower than or equal to
1.times.10.sup.-10 Pam.sup.3/second, entry of impurities such as
alkali metal or hydride into the oxide semiconductor film that is
being formed by a sputtering method can be reduced. Further, with
the use of the entrapment vacuum pump as an evacuation system,
counter flow of impurities, such as alkali metal, hydrogen atoms,
hydrogen molecules, water, a hydroxyl group, or hydride, from the
evacuation system can be reduced.
[0216] When the purity of the target is set to 99.99% or higher,
alkali metal, hydrogen atoms, hydrogen molecules, water, a hydroxyl
group, hydride, or the like mixed into the oxide semiconductor film
can be reduced. In addition, when the target is used, the
concentration of alkali metal such as lithium, sodium, or potassium
can be reduced in the oxide semiconductor film.
[0217] In order that hydrogen, a hydroxyl group, and moisture be
contained in the oxide semiconductor film as little as possible, it
is preferable that an impurity such as hydrogen or moisture that is
adsorbed on the substrate 700 be eliminated and exhausted by
preheating of the substrate 700, over which films up to the
insulating film 714 are formed, in a preheating chamber of the
sputtering apparatus, as pretreatment for film formation. The
temperature for the preheating is higher than or equal to
100.degree. C. and lower than or equal to 400.degree. C.,
preferably, higher than or equal to 150.degree. C. and lower than
or equal to 300.degree. C. As an evacuation unit, a cryopump is
preferably provided in the preheating chamber. Note that this
preheating treatment can be omitted. This preheating may be
similarly performed on the substrate 700 over which conductive
films 717 and 718 are formed before the formation of a gate
insulating film 719.
[0218] Note that etching for forming the oxide semiconductor film
715 may be dry etching, wet etching, or both dry etching and wet
etching. As an etching gas used for dry etching, a gas containing
chlorine (a chlorine-based gas such as chlorine (Cl.sub.2), boron
trichloride (BCl.sub.3), silicon tetrachloride (SiCl.sub.4), or
carbon tetrachloride (CCl.sub.4)) is preferably used.
Alternatively, a gas containing fluorine (a fluorine-based gas such
as carbon tetrafluoride (CF.sub.4), sulfur hexafluoride (SF.sub.6),
nitrogen trifluoride (NF.sub.3), or trifluoromethane (CHF.sub.3)),
hydrogen bromide (HBr), oxygen (O.sub.2), any of these gases to
which a rare gas such as helium (He) or argon (Ar) is added, or the
like can be used.
[0219] As the dry etching, parallel plate reactive ion etching
(RIE) or inductively coupled plasma (ICP) etching can be used. In
order to etch the film to have a desired shape, the etching
conditions (e.g., the amount of electric power applied to a coiled
electrode, the amount of electric power applied to an electrode on
the substrate side, and the electrode temperature on the substrate
side) are adjusted as appropriate.
[0220] As an etchant used for the wet etching, a mixed solution of
phosphoric acid, acetic acid, and nitric acid, or organic acid such
as citric acid or oxalic acid can be used. In this embodiment,
ITO-07N (produced by KANTO CHEMICAL CO., INC.) is used.
[0221] A resist mask used for forming the oxide semiconductor film
715 may be formed by an inkjet method. Formation of the resist mask
by an inkjet method needs no photomask; thus, manufacturing cost
can be reduced.
[0222] Note that it is preferable that reverse sputtering be
performed before the formation of a conductive film in a subsequent
step so that a resist residue and the like that attach onto
surfaces of the oxide semiconductor film 715 and the insulating
film 714 are removed.
[0223] Note that the oxide semiconductor film formed by sputtering
or the like contains a large amount of moisture or hydrogen
(including a hydroxyl group) as an impurity in some cases. Moisture
or hydrogen easily forms donor levels and thus serves as an
impurity in the oxide semiconductor. In one embodiment of the
present invention, in order to reduce impurities such as moisture
or hydrogen in the oxide semiconductor film (in order to perform
dehydration or dehydrogenation), the oxide semiconductor film 715
is subjected to heat treatment in a reduced- pressure atmosphere,
an inert gas atmosphere of nitrogen, a rare gas, or the like, an
oxygen gas atmosphere, or ultra-dry air (the moisture amount is 20
ppm (-55.degree. C. by conversion into a dew point) or less,
preferably 1 ppm or less, further preferably 10 ppb or less in the
case where measurement is performed by a dew point meter in a
cavity ring-down laser spectroscopy (CRDS) method).
[0224] By performing heat treatment on the oxide semiconductor film
715, moisture or hydrogen in the oxide semiconductor film 715 can
be eliminated. Specifically, heat treatment may be performed at a
temperature higher than or equal to 250.degree. C. and lower than
or equal to 750.degree. C., preferably higher than or equal to
400.degree. C. and lower than the strain point of the substrate.
For example, heat treatment may be performed at 500.degree. C. for
approximately 3 to 6 minutes. When RTA is used for the heat
treatment, dehydration or dehydrogenation can be performed in a
short time; thus, treatment can be performed even at a temperature
higher than the strain point of a glass substrate.
[0225] In this embodiment, an electrical furnace that is one of
heat treatment apparatuses is used.
[0226] Note that the heat treatment apparatus is not limited to an
electric furnace, and may have a device for heating an object by
heat conduction or heat radiation from a heating element such as a
resistance heating element. For example, an RTA (rapid thermal
anneal) apparatus such as a GRTA (gas rapid thermal anneal)
apparatus or an LRTA (lamp rapid thermal anneal) apparatus can be
used. An LRTA apparatus is an apparatus for heating an object to be
processed by radiation of light (an electromagnetic wave) emitted
from a lamp such as a halogen lamp, a metal halide lamp, a xenon
arc lamp, a carbon arc lamp, a high pressure sodium lamp, or a high
pressure mercury lamp. A GRTA apparatus is an apparatus for heat
treatment using a high-temperature gas. As the gas, an inert gas
which does not react with an object to be processed by heat
treatment, like nitrogen or a rare gas such as argon is used.
[0227] In the heat treatment, it is preferable that moisture,
hydrogen, and the like be not contained in nitrogen or a rare gas
such as helium, neon, or argon. The purity of nitrogen or the rare
gas such as helium, neon, or argon which is introduced into the
heat treatment apparatus is preferably 6N (99.9999%) or higher,
further preferably 7N (99.99999%) or higher (that is, the impurity
concentration is preferably 1 ppm or lower, further preferably 0.1
ppm or lower).
[0228] Through the above process, the concentration of hydrogen in
the oxide semiconductor film 715 can be reduced and the oxide
semiconductor film 715 can be highly purified. Thus, the oxide
semiconductor film can be stabilized. In addition, heat treatment
at a temperature lower than or equal to the glass transition
temperature makes it possible to form an oxide semiconductor film
with extremely low carrier density and a wide bandgap. Thus, the
transistor can be formed using a large substrate, so that mass
productivity can be improved. In addition, by using the oxide
semiconductor film in which the hydrogen concentration is reduced
and the purity is improved, it is possible to manufacture a
transistor with high withstand voltage and an extremely small
off-state current. The above heat treatment can be performed at any
time after the oxide semiconductor film is formed.
[0229] Note that the oxide semiconductor film may be either
amorphous or crystalline. As a crystalline oxide semiconductor
film, an oxide semiconductor film (c-axis aligned crystalline oxide
semiconductor film (CAAC-OS film)) including crystals with c-axis
orientation (CAAC) is also preferable because the effect of
improving the reliability of a transistor can be obtained.
[0230] Sputtering may be performed to form an oxide semiconductor
film including a CAAC-OS film. In order to obtain a CAAC-OS film by
sputtering, it is important to form hexagonal crystals in an
initial stage of deposition of an oxide semiconductor film and to
cause crystal growth from the hexagonal crystals as seed crystals.
In order to achieve this, it is preferable that the distance
between the target and the substrate be made longer (e.g., 150 mm
to 200 mm) and the substrate heating temperature be 100.degree. C.
to 500.degree. C., more preferably 200.degree. C. to 400.degree.
C., still preferably 250.degree. C. to 300.degree. C. In addition
to this, the deposited oxide semiconductor film is subjected to
heat treatment at a temperature higher than the substrate heating
temperature in the deposition. Thus, micro-defects in the film and
defects at the interface between stacked layers can be
repaired.
[0231] Next as illustrated in FIG. 14A, part of the conductive film
710 is exposed by formation of an opening by etching or the like in
the insulating film 713 and the insulating film 714, and then the
conductive film 717 in contact with the conductive film 710 in the
opening and also in contact with the oxide semiconductor film 715
and the conductive film 718 in contact with the oxide semiconductor
film 715 are formed. The conductive films 717 and 718 function as a
source and drain electrodes.
[0232] Specifically, the conductive films 717 and 718 can be formed
as follows: a conductive film is formed over the insulating film
714 by sputtering or vacuum evaporation so as to cover the opening,
and then, the conductive film is processed (patterned) into a
predetermined shape.
[0233] The conductive film which is to be the conductive films 717
and 718 can be formed using any of the following materials: an
element selected from aluminum, chromium, copper, tantalum,
titanium, molybdenum, and tungsten; an alloy containing any of
these elements as a component; an alloy film containing any of
these elements in combination; and the like. Alternatively, the
conductive film may have a structure in which a film of a
refractory metal such as chromium, tantalum, titanium, molybdenum,
or tungsten is stacked over or below a metal film of aluminum,
copper, or the like. Aluminum or copper is preferably used in
combination with a refractory metal material in order to avoid
problems with heat resistance and corrosion. As the refractory
metal material, molybdenum, titanium, chromium, tantalum, tungsten,
neodymium, scandium, yttrium, or the like can be used.
[0234] Further, the conductive film which is to be the conductive
films 717 and 718 may have a single-layer structure or a
stacked-layer structure of two or more layers. For example, a
single-layer structure of an aluminum film containing silicon, a
two-layer structure in which a titanium film is stacked over an
aluminum film, a three-layer structure in which a titanium film, an
aluminum film, and a titanium film are stacked in that order, and
the like can be given. A Cu--Mg--Al alloy, a Mo--Ti alloy, Ti, and
Mo have high adhesiveness with an oxide film. Therefore, for the
conductive films 717 and 718, a layered structure is employed in
which a conductive film containing a Cu--Mg--Al alloy, a Mo--Ti
alloy, Ti, or Mo is used for the lower layer and a conductive film
containing Cu is used for the upper layer; thus, the adhesiveness
between the insulating film 714, which is an oxide film, and the
conductive films 717 and 718 can be increased.
[0235] For the conductive film which is to be the conductive films
717 and 718, a conductive metal oxide may be used. As the
conductive metal oxide, indium oxide, tin oxide, zinc oxide, a
mixture of indium oxide and tin oxide, a mixture of indium oxide
and zinc oxide, or the conductive metal oxide material to which
silicon or silicon oxide is added can be used.
[0236] In the case where heat treatment is performed after
formation of the conductive film, the conductive film preferably
has heat resistance enough to withstand the heat treatment.
[0237] In this embodiment, each of the conductive films 717 and 718
is a 150-nm-thick tungsten film.
[0238] Note that materials and etching conditions are adjusted as
appropriate so that the oxide semiconductor film 715 is removed as
little as possible in etching of the conductive film. Depending on
the etching conditions, an exposed portion of the oxide
semiconductor film 715 is partly etched, so that a groove (a
depression portion) is formed in some cases.
[0239] In this embodiment, a tungsten film is used as the
conductive film which is to be the conductive films 717 and 718.
Therefore, wet etching can be selectively performed on the
conductive film using a solution (an ammonia hydrogen peroxide
mixture) containing ammonia and hydrogen peroxide water. As the
ammonia hydrogen peroxide mixture, specifically, a solution in
which hydrogen peroxide water of 31 wt %, ammonia water of 28 wt %,
and water are mixed at a volume ratio of 5:2:2 is used.
Alternatively, dry etching may be performed on the conductive film
with the use of a gas containing carbon tetrafluoride (CF.sub.4),
chlorine (Cl.sub.2), or oxygen.
[0240] In order to reduce the number of photomasks and steps in a
photolithography process, etching may be performed with the use of
a resist mask formed using a multi-tone mask through which light is
transmitted so as to have a plurality of intensities. A resist mask
formed using a multi-tone mask has a plurality of thicknesses and
can be changed in shape by etching; thus, the resist mask can be
used in a plurality of etching steps for processing films into
different patterns. Therefore, a resist mask corresponding to at
least two kinds of different patterns can be formed by one
multi-tone mask. Thus, the number of light-exposure masks can be
reduced and the number of corresponding photolithography steps can
be also reduced, whereby simplification of a process can be
achieved.
[0241] Further, an oxide conductive film functioning as a source
region and a drain region may be provided between the oxide
semiconductor film 715 and the conductive films 717 and 718
functioning as source and drain electrodes. The material of the
oxide conductive film preferably contains zinc oxide as a component
and preferably does not contain indium oxide. For such an oxide
conductive film, zinc oxide, zinc aluminum oxide, zinc aluminum
oxynitride, gallium zinc oxide, or the like can be used.
[0242] For example, in the case where the oxide conductive film is
formed, patterning for forming the oxide conductive film and
patterning for forming the conductive films 717 and 718 may be
performed concurrently.
[0243] With provision of the oxide conductive film functioning as a
source region and a drain region, resistance between the oxide
semiconductor film 715 and the conductive films 717 and 718 can be
lowered, so that the transistor can operate at high speed. In
addition, with provision of the oxide conductive film functioning
as a source region and a drain region, the withstand voltage of the
transistor can be increased.
[0244] Next, plasma treatment may be performed using a gas such as
N.sub.2O, N.sub.2, or Ar. By this plasma treatment, water or the
like adhering to an exposed surface of the oxide semiconductor film
is removed. Plasma treatment may be performed using a mixture gas
of oxygen and argon as well.
[0245] After the plasma treatment, as illustrated in FIG. 14B, the
gate insulating film 719 is formed so as to cover the conductive
films 717 and 718 and the oxide semiconductor film 715. Then, a
gate electrode 720 is formed over the gate insulating film 719 so
as to overlap with the oxide semiconductor film 715, and a
conductive film 721 is formed over the conductive film 719 so as to
overlap with the conductive film 717.
[0246] The gate insulating film 719 can be formed using a material
and a layered structure which are similar to those of the gate
insulating film 703. Note that the gate insulating film 719
preferably contains impurities such as moisture or hydrogen as
little as possible, and the gate insulating film 719 may be formed
using a single-layer insulating film or a plurality of insulating
films stacked. When hydrogen is contained in the gate insulating
film 719, hydrogen enters the oxide semiconductor film 715 or
oxygen in the oxide semiconductor film 715 is extracted by
hydrogen, whereby the oxide semiconductor film 715 has lower
resistance (n-type conductivity); thus, a parasitic channel might
be formed. Thus, it is important that a deposition method in which
hydrogen is not used be employed in order to form the gate
insulating film 719 containing hydrogen as little as possible. A
material having a high barrier property is preferably used for the
gate insulating film 719. As the insulating film having a high
barrier property, a silicon nitride film, a silicon nitride oxide
film, an aluminum nitride film, an aluminum nitride oxide film, or
the like can be used, for example. When a stack of a plurality of
insulating films is used, an insulating film having low proportion
of nitrogen such as a silicon oxide film or a silicon oxynitride
film is formed on a side which is closer to the oxide semiconductor
film 715 than the insulating film having a high barrier property.
Then, the insulating film having a high barrier property is formed
so as to overlap with the conductive films 717 and 718 and the
oxide semiconductor film 715 with the insulating film having low
proportion of nitrogen sandwiched therebetween. When the insulating
film having a high barrier property is used, impurities such as
moisture or hydrogen can be prevented from entering the oxide
semiconductor film 715, the gate insulating film 719, or the
interface between the oxide semiconductor film 715 and another
insulating film and the vicinity thereof. In addition, the
insulating film having lower proportion of nitrogen, such as a
silicon oxide film or a silicon oxynitride film, is formed so as to
be in contact with the oxide semiconductor film 715, so that the
insulating film having a high barrier property can be prevented
from being in direct contact with the oxide semiconductor film
715.
[0247] In this embodiment, a silicon oxynitride film with a
thickness of 30 nm which is formed by a sputtering method is used
as the gate insulating film 719. The substrate temperature at
deposition may be higher than or equal to room temperature and
lower than or equal to 400.degree. C., and in this embodiment is
300.degree. C.
[0248] After the gate insulating film 719 is formed, heat treatment
may be performed. The heat treatment is performed in a nitrogen
atmosphere, ultra-dry air, or a rare gas (such as argon or helium)
atmosphere preferably at a temperature higher than or equal to
200.degree. C. and lower than or equal to 400.degree. C., for
example, higher than or equal to 250.degree. C. and lower than or
equal to 350.degree. C. It is preferable that the water content in
the gas be 20 ppm or less, preferably 1 ppm or less, further
preferably 10 ppb or less. In this embodiment, for example, heat
treatment is performed at 250.degree. C. for one hour in a nitrogen
atmosphere. Alternatively, RTA treatment for a short time at a high
temperature may be performed before the formation of the conductive
films 717 and 718 in a manner similar to that of the heat treatment
performed on the oxide semiconductor film for reduction of moisture
or hydrogen. Even when oxygen vacancies are generated in the oxide
semiconductor film 715 by the heat treatment performed on the oxide
semiconductor film 715, oxygen is supplied to the oxide
semiconductor film 715 from the gate insulating film 719 by
performing heat treatment after provision of the gate insulating
film 719 containing oxygen. By the supply of oxygen to the oxide
semiconductor film 715, oxygen vacancies that serve as donors can
be reduced in the oxide semiconductor film 715 and the
stoichiometric composition can be satisfied. It is preferable that
the proportion of oxygen in the oxide semiconductor film is higher
than that in the stoichiometric composition. As a result, the oxide
semiconductor film 715 can be made substantially i-type and
variations in electric characteristics of transistors due to oxygen
vacancies can be reduced; thus, electric characteristics can be
improved. There is no particular limitation on the timing of this
heat treatment as long as it is after the formation of the gate
insulating film 719. When this heat treatment also serves as heat
treatment in another step (e.g., heat treatment at the time of
formation of a resin film or heat treatment for lowering the
resistance of a transparent conductive film), the oxide
semiconductor film 715 can be made substantially i-type without an
increase in the number of steps.
[0249] Further, oxygen vacancies that serve as donors in the oxide
semiconductor film 715 may be reduced by performing heat treatment
on the oxide semiconductor film 715 in an oxygen atmosphere so that
oxygen is added to the oxide semiconductor. The heat treatment is
performed at, for example, higher than or equal to 100.degree. C.
and lower than 350.degree. C., preferably higher than or equal to
150.degree. C. and lower than 250.degree. C. It is preferable that
an oxygen gas used for the heat treatment in an oxygen atmosphere
do not include water, hydrogen, or the like. The purity of the
oxygen gas which is introduced into a heat treatment apparatus is
preferably 6N (99.9999%) or higher, further preferably 7N
(99.99999%) or higher (i.e., the impurity concentration in the
oxygen is preferably 1 ppm or lower, further preferably 0.1 ppm or
lower).
[0250] Alternatively, oxygen may be added to the oxide
semiconductor film 715 by an ion implantation method, an ion doping
method, or the like so that oxygen vacancies that serve as donors
are reduced. For example, oxygen made to be plasma with a microwave
of 2.45 GHz may be added to the oxide semiconductor film 715.
[0251] The gate electrode 720 and the conductive film 721 can be
formed in such a manner that a conductive film is formed over the
gate insulating film 719 and then is patterned. The gate electrode
720 and the conductive film 721 can be formed using a material
similar to that of the gate electrode 704 or the conductive films
717 and 718.
[0252] The thickness of each of the gate electrode 720 and the
conductive film 721 is 10 nm to 400 nm, preferably 100 nm to 300
nm. In this embodiment, after a conductive film with a thickness of
150 nm for the gate electrode is formed by a sputtering method
using a tungsten target, the conductive film is processed
(patterned) into a desired shape by etching, whereby the gate
electrode 720 and the conductive film 721 are formed. Note that a
resist mask may be formed by an inkjet method. Formation of the
resist mask by an inkjet method needs no photomask; thus,
manufacturing cost can be reduced.
[0253] Through the above steps, the transistor 106t is formed.
[0254] Note that a portion where the conductive film 717 and the
conductive film 721 overlap with each other with the gate
insulating film 719 provided therebetween corresponds to the
capacitor 111. Although the capacitor 112 is not illustrated in
this embodiment, similarly to the capacitor 111, the capacitor 112
can be formed by providing, besides the conductive film 721, a
conductive film which overlaps with the conductive film 717 with
the gate insulating film 719 provided therebetween over the gate
insulating film 719.
[0255] Although the transistor 106t is described as a single-gate
transistor, a multi-gate transistor including a plurality of
channel formation regions can be formed when a plurality of gate
electrodes which are electrically connected to each other are
included, if needed.
[0256] Note that an insulating film which is in contact with the
oxide semiconductor film 715 (in this embodiment, corresponding to
the insulating film 714 and the gate insulating film 719) may be
formed using an insulating material containing an element that
belongs to Group 13 and oxygen. Many of oxide semiconductor
materials contain Group 13 elements, and an insulating material
containing a Group 13 element works well with oxide semiconductors.
By using such an insulating material containing a Group 13 element
for the insulating film in contact with the oxide semiconductor
film, the state of an interface with the oxide semiconductor film
can be kept well.
[0257] An insulating material containing a Group 13 element is an
insulating material containing one or more Group 13 elements.
Examples of the insulating material containing a Group 13 element
include gallium oxide, aluminum oxide, aluminum gallium oxide, and
gallium aluminum oxide. Here, aluminum gallium oxide refers to a
material in which the amount of aluminum is larger than that of
gallium in atomic percent, and gallium aluminum oxide refers to a
material in which the amount of gallium is larger than or equal to
that of aluminum in atomic percent.
[0258] For example, in the case where an insulating film is formed
in contact with an oxide semiconductor film containing gallium,
when a material containing gallium oxide is used for the insulating
film, favorable characteristics can be kept at the interface
between the oxide semiconductor film and the insulating film. For
example, when the oxide semiconductor film and the insulating film
containing gallium oxide are provided in contact with each other,
pileup of hydrogen at the interface between the oxide semiconductor
film and the insulating film can be reduced. Note that a similar
effect can be obtained in the case where an element in the same
group as a constituent element of the oxide semiconductor is used
in an insulating film. For example, it is effective to form an
insulating film with the use of a material containing aluminum
oxide. Note that aluminum oxide has a property of not easily
transmitting water. Thus, it is preferable to use a material
including aluminum oxide in terms of preventing entry of water to
the oxide semiconductor film.
[0259] The insulating film in contact with the oxide semiconductor
film 715 preferably contains oxygen in a proportion higher than
that in the stoichiometric composition by heat treatment in an
oxygen atmosphere or oxygen doping. "Oxygen doping" refers to
addition of oxygen into a bulk. Note that the term "bulk" is used
in order to clarify that oxygen is added not only to a surface of a
thin film but also to the inside of the thin film. In addition,
"oxygen doping" includes "oxygen plasma doping" in which oxygen
which is made to be plasma is added to a bulk. The oxygen doping
may be performed by ion implantation or ion doping.
[0260] By oxygen doping, an insulating film that includes a region
where the proportion of oxygen is higher than that in the
stoichiometric composition can be formed. When the insulating film
including such a region is in contact with the oxide semiconductor
film, excess oxygen in the insulating film is supplied to the oxide
semiconductor film, and oxygen vacancies in the oxide semiconductor
film or at the interface between the oxide semiconductor film and
the insulating film are reduced. Thus, the oxide semiconductor film
can be an i-type or substantially i-type oxide semiconductor.
[0261] The insulating film including a region where the proportion
of oxygen is higher than that in the stoichiometric composition may
be applied to either the insulating film placed on an upper side of
the oxide semiconductor film or the insulating film placed on a
lower side of the oxide semiconductor film of the insulating films
which are in contact with the oxide semiconductor film 715;
however, it is preferable to apply such an insulating film to both
the insulating films which are in contact with the oxide
semiconductor film 715. The above effect can be enhanced with a
structure where the oxide semiconductor film 715 is sandwiched
between the insulating films each including a region where the
proportion of oxygen is higher than that in the stoichiometric
composition, which are used as the insulating films in contact with
the oxide semiconductor film 715 and positioned on the upper side
and the lower side of the oxide semiconductor film 715.
[0262] The insulating films on the upper side and the lower side of
the oxide semiconductor film 715 may contain the same constituent
element or different constituent elements. The insulating film in
contact with the oxide semiconductor film 715 may be a stack of
insulating films each of which includes a region where the
proportion of oxygen is higher than that in the stoichiometric
composition.
[0263] Next, as illustrated in FIG. 14C, an insulating film 722 is
formed so as to cover the gate insulating film 719, the conductive
film 721, and the gate electrode 720. The insulating film 722 can
be formed by PVD, CVD, or the like. The insulating film 722 can be
formed using a material including an inorganic insulating material
such as silicon oxide, silicon oxynitride, silicon nitride, hafnium
oxide, gallium oxide, or aluminum oxide. Note that for the
insulating film 722, a material with a low dielectric constant or a
structure with a low dielectric constant (e.g., a porous structure)
is preferably used. When the dielectric constant of the insulating
film 722 is lowered, parasitic capacitance generated between
wirings or electrodes can be reduced, which results in higher speed
operation. Although the insulating film 722 has a single-layer
structure in this embodiment, one embodiment of the present
invention is not limited to this structure. The insulating film 722
may have a stacked-layer structure of two or more layers.
[0264] Next, an opening 725 is formed in the gate insulating film
719 and the insulating film 722, so that part of the conductive
film 721 is exposed. After that, a wiring 726 which is in contact
with the conductive film 721 through the opening 725 is formed over
the insulating film 722.
[0265] A conductive film is formed by PVD or CVD and then is
patterned, so that the wiring 726 is formed. As a material of the
conductive film, an element selected from aluminum, chromium,
copper, tantalum, titanium, molybdenum, and tungsten; an alloy
containing any of these elements as a component; or the like can be
used. Further, one or more materials selected from manganese,
magnesium, zirconium, beryllium, neodymium, and scandium may be
used.
[0266] In this embodiment, a conductive film formed by stacking a
titanium film with a thickness of about 50 nm, an aluminum film
with a thickness of about 200 nm, and a titanium film with a
thickness of about 50 nm in this order by a sputtering method is
used as the wiring 726. Here, the titanium film has a function of
reducing an oxide film (e.g., a native oxide film) formed on the
surface over which the titanium film is formed, to decrease the
contact resistance with the lower electrode or the like (here, the
conductive film 718). In addition, hillock of the aluminum film can
be prevented. A copper film may be formed by a plating method after
a barrier film of titanium, titanium nitride, or the like is
formed.
[0267] Next, an insulating film 727 is formed so as to cover the
wiring 726. Through the series of steps, the PLD can be
manufactured.
[0268] Note that in the manufacturing method, the conductive films
717 and 718 functioning as source and drain electrodes are formed
after the formation of the oxide semiconductor film 715. Thus, as
illustrated in FIG. 14B, in the transistor 106t obtained by the
manufacturing method, the conductive films 717 and 718 are formed
over the oxide semiconductor film 715. However, in the transistor
106t, the conductive films functioning as source and drain
electrodes may be formed below the oxide semiconductor film 715,
that is, between the oxide semiconductor film 715 and the
insulating film 714.
[0269] In FIG. 14C, the conductive film 710 and the conductive film
717 correspond to the node 110 in FIG. 6A. In addition, the
conductive film 721 corresponds to the wiring 108 in FIG. 6A. Next,
a cross-sectional view of a semiconductor device manufactured based
on the above PLD is illustrated in FIG. 15. In the semiconductor
device in FIG. 15, layers up to the insulating film 714 can have
the same structure as those in the PLD. An opening is formed in the
insulating films 713 and 714, and a wiring 800 connected to the
conductive film 710 through the opening is provided over the
insulating film 714. The wiring 800 is preferably formed using a
material and a layered structure similar to those of the conductive
film 718. In addition, the layout of the wiring 800 is preferably
similar to the layout of the conductive film 718. When the wiring
800 has such a structure, parasitic capacitance between the wiring
800 and the programmable logic element in the semiconductor device
can be close to the parasitic capacitance between the memory array
and the programmable logic element in the PLD. Consequently, power
consumption of the semiconductor device can be estimated accurately
at the stage of testing the PLD.
[0270] This embodiment can be implemented in appropriate
combination with any of the other embodiments.
Embodiment 5
[0271] In this embodiment, examples of the layout of the memory
elements 103 and examples of the layout in which the memory
elements 103 are each replaced with wirings are described.
[0272] FIG. 17A illustrates an example of the layout of the memory
elements 103a and 103b in FIG. 6A. The memory elements 103a and
103b in FIG. 17A include a conductive film 107c functioning as the
wiring 107, a conductive film 108c functioning as the wiring 108, a
conductive film 109c functioning as the wiring 109, and a
conductive film 150c functioning as the wiring 150. The conductive
film 107c also functions as one of the source terminal and the
drain terminal of the transistor 106t. The conductive film 150c
also functions as the gate electrode of the transistor 106t.
[0273] The memory elements 103a and 103b include a conductive film
170 and a conductive film 110c connected to the conductive film
170. The conductive film 170 functions as the other of the source
terminal and the drain terminal of the transistor 106t.
[0274] The conductive film 110c functions as part of the node 110.
Although not illustrated, the conductive film 110c is electrically
connected to the programmable logic element provided below the
memory elements 103a and 103b. Note that in one embodiment of the
present invention, the node 110 has a function of establishing
electrical connection between the memory array and the programmable
logic element; accordingly, it can be said that one or more
conductive films functioning as the node 110 are included in either
or both the memory array and the programmable logic element.
[0275] A region where the conductive film 108c and the conductive
film 110c overlap with each other with the gate insulating film
(not shown) therebetween functions as the capacitor 111. A region
where the conductive film 109c and the conductive film 110c overlap
with each other with the gate insulating film (not shown)
therebetween functions as the capacitor 112.
[0276] FIG. 17B illustrates an example of the layout in the case
where the memory elements 103a and 103b in FIG. 17A are each
replaced with the conductive film 110c, the conductive film 108c,
and the conductive film 109c.
[0277] In the case exemplified in FIG. 17B, the conductive film
108c is selected from the conductive films 108c and 109c, which are
provided instead of the memory element 103a, by the configuration
data to be connected to the conductive film 110c. Further, the
conductive film 109c is selected from the conductive films 108c and
109c, which are provided instead of the memory element 103b, by the
configuration data to be connected to the conductive film 110c.
[0278] FIG. 17B illustrates the case where the conductive film 107c
and the conductive film 170 are provided as well as the conductive
film 110c, the conductive film 108c, and the conductive film 109c
instead of the memory element 103a; however, the conductive film
107c and the conductive film 170 are not necessarily provided in
the semiconductor device. Note that when the conductive film 107c
and the conductive film 170 are provided in the semiconductor
device as in the PLD, power consumption or operation frequency of
the semiconductor device due to parasitic capacitance can be
estimated more accurately at the stage of testing the PLD.
[0279] FIGS. 17A and 17B illustrate the case where the transistor
106t is a bottom-gate transistor. Accordingly, in FIG. 17A, the
conductive film 150c and the conductive film 110c are formed in a
first layer, and the conductive film 107c, the conductive film
108c, the conductive film 109c, and the conductive film 170 are
formed in a second layer above the first layer.
[0280] FIGS. 18A and 18B illustrate the layout of the memory
elements 103a and 103b and the layout in the case where the memory
elements 103a and 103b are each replaced with wirings, as examples
in the case where the transistor 106t is a top-gate transistor. In
FIGS. 18A and 18B, the conductive film 107c, the conductive film
108c, the conductive film 109c, and the conductive film 170 are
formed in a first layer, and the conductive film 150c and the
conductive film 110c are formed in a second layer above the first
layer.
[0281] FIG. 19A illustrates an example of the layout of the memory
elements 103a and 103b in FIG. 7A. The memory elements 103a and
103b in FIG. 19A include the conductive film 107c functioning as
the wiring 107, the conductive film 108c functioning as the wiring
108, the conductive film 109c functioning as the wiring 109, and
the conductive film 150c functioning as the wiring 150. The
conductive film 107c functions as one of the source terminal and
the drain terminal of the transistor 106t and also functions as one
of the source terminal and the drain terminal of the transistor
151t. The conductive film 108c also functions as the other of the
source terminal and the drain terminal of the transistor 151t. The
conductive film 150c also functions as the gate electrode of the
transistor 106t.
[0282] The memory elements 103a and 103b include a conductive film
171 and the conductive film 110c connected to the conductive film
171. The conductive film 171 functions as the other of the source
terminal and the drain terminal of the transistor 106t. The
conductive film 110c functions as the gate electrode of the
transistor 151t.
[0283] The conductive film 110c also functions as part of the node
110. Although not illustrated, the conductive film 110c is
electrically connected to the programmable logic element provided
below the memory elements 103a and 103b.
[0284] A region where the conductive film 108c and the conductive
film 110c overlap with each other with the gate insulating film
(not shown) therebetween functions as the capacitor 111. A region
where the conductive film 109c and the conductive film 110c overlap
with each other with the gate insulating film (not shown)
therebetween functions as the capacitor 112.
[0285] FIG. 19B illustrates an example of the layout in the case
where the memory elements 103a and 103b in FIG. 19A are each
replaced with the conductive film 110c, the conductive film 108c,
and the conductive film 109c.
[0286] In the case exemplified in FIG. 19B, the conductive film
108c is selected from the conductive films 108c and 109c, which are
provided instead of the memory element 103a, by the configuration
data to be connected to the conductive film 110c. Further, the
conductive film 109c is selected from the conductive films 108c and
109c, which are provided instead of the memory element 103b, by the
configuration data to be connected to the conductive film 110c.
[0287] FIG. 19B illustrates the case where the conductive film 107c
and the conductive film 171 are provided as well as the conductive
film 110c, the conductive film 108c, and the conductive film 109c
instead of the memory element 103a; however, the conductive film
107c and the conductive film 171 are not necessarily provided in
the semiconductor device. Note that when the conductive film 107c
and the conductive film 171 are provided in the semiconductor
device as in the PLD, power consumption or operation frequency of
the semiconductor device due to parasitic capacitance can be
estimated more accurately at the stage of testing the PLD.
[0288] FIGS. 19A and 19B illustrate the case where the transistor
106t and the transistor 151t are bottom-gate transistors.
Accordingly, in FIG. 19A, the conductive film 150c and the
conductive film 110c are formed in a first layer, and the
conductive film 107c, the conductive film 108c, the conductive film
109c, and the conductive film 171 are formed in a second layer
above the first layer.
[0289] FIGS. 20A and 20B illustrate the layout of the memory
elements 103a and 103b and the layout in the case where the memory
elements 103a and 103b are each replaced with wirings, as examples
in the case where the transistor 106t and the transistor 151t are
top-gate transistors. In FIGS. 20A and 20B, the conductive film
107c, the conductive film 108c, the conductive film 109c, and the
conductive film 171 are formed in a first layer, and the conductive
film 150c and the conductive film 110c are formed in a second layer
above the first layer.
[0290] This embodiment can be implemented in appropriate
combination with any of the other embodiments.
Embodiment 6
[0291] The semiconductor device or the programmable logic device
according to one embodiment of the present invention can be used
for display devices, personal computers, or image reproducing
devices provided with recording media (typically, devices which
reproduce the content of recording media such as digital versatile
discs (DVDs) and have displays for displaying the reproduced
images). Other examples of electronic devices that can include the
semiconductor device or the programmable logic device according to
one embodiment of the present invention are mobile phones, game
machines including portable game machines, personal digital
assistants, e-book readers, cameras such as video cameras and
digital still cameras, goggle-type displays (head mounted
displays), navigation systems, audio reproducing devices (e.g., car
audio systems and digital audio players), copiers, facsimiles,
printers, multifunction printers, automated teller machines (ATM),
and vending machines. FIGS. 16A to 16F illustrate specific examples
of these electronic devices.
[0292] FIG. 16A illustrates a portable game machine, which includes
a housing 5001, a housing 5002, a display portion 5003, a display
portion 5004, a microphone 5005, speakers 5006, an operation key
5007, a stylus 5008, and the like. Note that although the portable
game machine in FIG. 16A includes the two display portions 5003 and
5004, the number of display portions included in the portable game
machine is not limited to two.
[0293] FIG. 16B illustrates a personal digital assistant, which
includes a first housing 5601, a second housing 5602, a first
display portion 5603, a second display portion 5604, a joint 5605,
an operation key 5606, and the like. The first display portion 5603
is provided in the first housing 5601, and the second display
portion 5604 is provided in the second housing 5602. The first
housing 5601 and the second housing 5602 are connected to each
other with the joint 5605, and an angle between the first housing
5601 and the second housing 5602 can be changed with the joint
5605. An image on the first display portion 5603 may be switched
depending on the angle between the first housing 5601 and the
second housing 5602 at the joint 5605. A display device with a
position input function may be used as at least one of the first
display portion 5603 and the second display portion 5604. Note that
the position input function can be added by provision of a touch
panel in a display device. Alternatively, the position input
function can be added by provision of a photoelectric conversion
element called a photosensor in a pixel area of a display
device.
[0294] FIG. 16C illustrates a laptop personal computer, which
includes a housing 5401, a display portion 5402, a keyboard 5403, a
pointing device 5404, and the like.
[0295] FIG. 16D illustrates an electric refrigerator-freezer, which
includes a housing 5301, a door for a refrigerator 5302, a door for
a freezer 5303, and the like.
[0296] FIG. 16E illustrates a video camera, which includes a first
housing 5801, a second housing 5802, a display portion 5803,
operation keys 5804, a lens 5805, a joint 5806, and the like. The
operation keys 5804 and the lens 5805 are provided in the first
housing 5801, and the display portion 5803 is provided in the
second housing 5802. The first housing 5801 and the second housing
5802 are connected to each other with the joint 5806, and an angle
between the first housing 5801 and the second housing 5802 can be
changed with the joint 5806. An image on the display portion 5803
may be switched depending on the angle between the first housing
5801 and the second housing 5802 at the joint 5806.
[0297] FIG. 16F illustrates an ordinary motor vehicle, which
includes a car body 5101, wheels 5102, a dashboard 5103, lights
5104, and the like.
[0298] This embodiment can be combined with any of the other
embodiments as appropriate.
[0299] This application is based on Japanese Patent Application
serial no. 2012-026105 filed with Japan Patent Office on Feb. 9,
2012, the entire contents of which are hereby incorporated by
reference.
* * * * *